Ikaruga (斑鳩) is a vertical-scrolling shooter developed and published by Treasure in December 2001 for the Sega NAOMI arcade system. During development, the game was referred to as ‘Project RS-2’, owing to its predecessor Radiant Silvergun, and as such it is considered to be its spiritual sequel, even though the two games differ considerably in terms of mechanics and visual style. Ikaruga is famous for its polarity system: enemies and bullets are either black or white, while the player’s ship has the ability to switch polarity between the two colours with the press of a button. A similar feature was already implemented to a lesser extent by the arcade shooter Great Mahou Daisakusen, but with Ikaruga being in development when it came out, the inspiration for its polarity mechanic is probably to be found elsewhere: some have mentioned Treasure’s Silhouette Mirage, but game director Hiroshi Iuchi himself  has spoken of its connection with the defensive system of Sega Saturn’s game Shinrei Jusatsushi Taromaru, to which he contributed to some extent.
Ikaruga enjoyed critical and commercial success for the genre’s standards and over the years has been ported to several home consoles (Sega Dreamcast, Nintendo GameCube and Switch, Xbox Live Arcade, Sony PlayStation 4) and online platforms (NESiCAxLive and Steam), with varying feature sets and fidelity to the original version (see the version differences section).
In general, Ikaruga is considered to be a very methodical shooting game. It punishes carefree blasting and frequent improvisation, while placing emphasis on rigorous routing and execution.
Most of Ikaruga’s storyline is not presented in-game, but can be gathered from texts included in some of the ported versions and related inserts (game manuals, bonus modes on the DC and GC versions, a text file accessible by inserting the DC gd-rom into a computer disc drive) . Here’s a short summary of the story preceding the events in the game:
“Sometime in the past, a woman esper named Hourai Tenro, ruler of the insular country of Hourai, unhearted a mysterious object from deep within the earth. Known as the Stone-Like, the object seemed to have a god-like quality and emanated an enormous amount of energy. After fitting a restrictive device to it, she managed to harness its power and proceeded to storm and conquer other nations along with her followers, claiming to be the ‘Chosen Ones’ to unite all the countries in the name of peace. A resistance group known as the ‘Tenkaku’ attempted to fight back, but lost battle after battle until only one member survived, the strong-willed Shinra [Player 1].
Refusing to call it quits, Shinra built a makeshift aircraft that he named Shirasagi and took off on a lone sortie against Hourai’s forces. He managed to make his way through numerous enemies until he was faced with the Eboshidori ‘Butsutekkai’, piloted by Hourai’s general Asami. After a fierce battle, Shinra was ultimately defeated and crash landed on a remote village nearby, inhabited by elderly people who were exiled after Hourai’s conquests - the Village of the Grosbeak (‘Ikaruga no Sato’). Shinra was recovered from the wreckage and nursed back to health. Unwilling to live with regret, he renewed his pledge to defeat Hourai, so the village elders entrusted him with a technological marvel built by former engineering genius Amanai along with the elder Kazamori: an aircraft capable of switching polarity and absorbing bullets, which was given the village’s name, Ikaruga. Thanks to the unique features of his new ship, Shinra was then able to confront general Asami’s Butsutekkai on equal terms, blocking his foray on the village and driving him away.
Soon after, Shinra is joined by Kagari [Player 2], a woman who originally fought for Hourai but changed side after being shot down and then spared by Shinra and the villagers. A formidable pilot herself, she manages to convince Amanai to upgrade her ship, the Ginkei, to Ikaruga’s capabilities. Firmly determined to bring back freedom, the two combatants set off to defeat Hourai Tenro’s forces and destroy the source of her powers... ”
The gameplay of Ikaruga revolves around the black and white polarity system, which entails the following:
- bullets are either black or white, and the player’s ship can freely switch between the two polarities: bullets of the opposite colour will destroy it, while those of its own colour will be absorbed (and fill up a power gauge)
- enemies are also either black or white, and when destroyed can release revenge bullets of their own colour, depending on the game’s difficulty mode (see the modes section)
- the offensive weapons are of the same polarity as the ship and deal double damage to enemies of the opposite colour
- enemies killed in groups of three of the same colour make a chain, which yields a varying amount of points up to a maximum value (‘max chain’ - see the scoring section)
In order to advance in the game, the player has to get familiar with switching polarity back and forth according to on-screen bullets, potential revenge bullets (if any) and, eventually, the polarity of the enemies (in order to deal more damage). Depending on the game section, speedkilling enemies can spawn additional ones, which potentially allows for more chains. There are no power-ups or items, nor a rank system (although some sections are toned down a bit when a life is lost).
Ikaruga is generally played with a three-button setup: A for firing, B for changing polarity and C for releasing energy. However, the arcade version’s setup was designed to be two-button (the third one being optional), with the energy release to be triggered with A+B.
Tapping the fire button will fire off a single shot. This shot type is used when one wants to take down specific enemies, which is often needed for chaining. Customized control set-ups may be equipped with an auto-fire button, allowing for a continuous single-shot stream which can be useful in some sections.
Holding the fire button down will fire off a double-shot stream. This is the main shot type of the game. One pair of projectiles from a double-shot stream causes the same damage as one single shot (consequently, while a single shot takes down one-hit popcorn enemies of the same polarity, a single projectile from a double-shot stream does not). As it is natural to expect, moving laterally while firing will make the bullet stream skew in the direction opposite to the movement. Finally, moving towards an enemy while it's being hit will speed up the collision of the bullets that are in between the ship and the enemy thus slightly increasing the damage per unit of time for a brief moment (the opposite applies when moving away from the enemy).
When the power gauge is at least partially filled up, pressing the relevant button will trigger the energy release, which consists of a varying number of homing lasers. The number goes from one to twelve, depending on the status of the power gauge (it is made up of twelve squares, each one representing a laser and taking ten bullets to fill up). One laser inflicts as much damage as five single shots. The energy release is not a panic bomb: it generally does not wipe out all the enemies that are on screen and can actually result in losing a life if the player changes polarity immediately after and is hit by revenge bullets (if any). It is, instead, a general use weapon (there are no score penalties attached), which is very useful for killing off larger enemies and damaging bosses quickly.
If used carefully, the energy release is also an invaluable asset for racking up chains. In order to preserve the chain through an energy release, players typically use it on clusters of enemies of the same polarity. However, it is definitely possible to chain both black and white enemies with a single release, since the lasers hit their targets in sequence. Here’s some insights on the logic behind the lasers’ behaviour:
- the lasers hit enemies according to their proximity to the path they travel along, which always goes from the rear and lateral side of the ship to the front and eventually back below it. Therefore, enemies immediately below or next to the ship are wiped out first, followed by the enemies that are in front of it and then those that are farther below
- the lasers are ejected from the ship stacked one on top of the other, with upper ones reaching out first. However, the upper lasers are generally not the first to hit their target, since they tend to pass by the first enemies they cross in their path (more so than the other lasers), pursuing their target only after doing a turnaround
- the lasers move at a varying speed: slower when turning around, faster when going straight
- if there is a large enemy on-screen, all the lasers generally tend to flock to it, ignoring smaller enemies
- if their original target is taken down or moves away, the lasers can either redirect to another enemy or just fly off for good, depending on the section and/or other factors
- if there are multiple enemies both next or below and in front of the ship (more than what the lasers can target), usually the energy release takes down a few of them from each area
- there might be some instance where a given energy release would appear to have a bias toward keeping chain integrity, but there is no actual evidence in support of this, and any such case is likely to be interpreted as normal behaviour after taking into account some of the points above or other idiosyncrasies of the energy release mechanic
While this is likely to be just a partial description of the logic behind energy releases, it must be noted that the lasers’ behaviour is always deterministically based on the type and position of the enemies relative to the player’s ship at the time of their release - there are no random elements to it, therefore once found out that a release can be used to chain some enemies in a given section, its behaviour will stay consistent if the conditions are replicated closely enough.
Arcade mode is the standard game mode and is the one that has been described up to now. However, every ported version of Ikaruga also features a ‘Prototype mode’, so called because it represents the game concept as originally designed by the developers .
This mode differs from arcade for having limited ammos, which are used up by firing off either the main shots or the homing lasers; the stock is replenished by absorbing bullets and is tracked by a counter which goes up to 999 (also replacing the arcade mode’s power gauge). Firing a single shot uses up two ammos (same for a single pair of double-shot) and homing lasers require ten ammos each (a full release taking 120 off the stock). Each absorbed bullet provides three ammos, and sitting on a laser beam will fill up the reserves in just a few seconds. If the reserves are depleted, the ship will only fire a shot with an extremely limited range, until some stock is restored.
Except for easy difficulty (see below), basic bullet-eating skills are generally enough to avert running out of ammos; in fact, it is quite common to get to the stage bosses with substantial reserves. In this case, the battle will clearly end in just a few seconds, thanks to the ability of launching multiple full releases one after the other that is unique to this game mode. However, it is worth noting that the different release mechanic also has a (comparatively small) downside with respect to the arcade mode - that is, having a full release always in stock makes it impossible to use in situations where optimal scoring strategies would require to take down just a few specific enemies (in order to keep the chain going).
Each game mode can be played on three difficulty levels, which differ in this way:
- Easy: enemies never release revenge bullets when killed. Some sections have less enemies and bullets than on normal and all three forms of the last chapter’s boss have less health
- Normal: enemies of the same polarity as the player release revenge bullets when killed (increasing in number depending on the enemy’s health bar - larger, more resistant enemies release more bullets)
- Hard: enemies always release revenge bullets when killed (though those of opposite polarity than the player only release half the number of bullets, eventually rounded down). Some sections have more bullets than on normal and the final form of the last chapter’s boss has more health (it also fires off its homing lasers at double the frequency, making it a real challenge to milk for score without dying)
Also, in prototype mode the player starts each chapter with a varying supply of ammos depending on the difficulty: 500 on easy, 300 on normal, 100 on hard. The initial stock doesn’t make much difference in terms of the overall balance of the mode, with the player often having to put up with very low or even no reserves on easy difficulty (due to the lack of revenge bullets).
The game can also be played on 2P mode. Ikaruga, with its polarity-based system and neatly symmetrical enemy patterns, lends itself very well to being played in 2P mode. Some game versions allow for cooperative gaming over the internet or have an option for double-play (for players that rise to the challenge of controlling both ships solo).
Lastly, while technically not representing a different mode, it is possible to finish the entire game without firing a single bullet: the pacifist player is rewarded with a ‘Dot Eater’ rank on the breakdown at the end of each stage.
The scoring system of Ikaruga is mainly centered around chaining enemies, but there are more ways to rack up points. Here they are listed in order of decreasing relevance:
- Chaining: taking down three enemies of the same polarity in succession will yield a chain. Each following chain can be of the same or of the opposite colour, and can be added immediately after or minutes away from the previous one: what matters is only that the enemies are killed in groups of three. Every destructible enemy that appears in the game has a polarity and can be chained (with the only exception of the parts of which main bosses are made of). The first chains reward the player with a varying amount of points, starting with a value of 100 points, then 200, 400 and so on, doubling each time up to 25600 (ninth chain and over). At each additional chain worth 25600 points, a robotic voice can be heard uttering either ‘Max Chain’, ‘Excellent’ or ‘Splendid’, letting you know how awesome you are. The chain is broken when the player fails to kill enemies in groups of three of the same colour or dies, and resets at the start of each stage.
In order to score more points, players try to chain as many enemies as possible (by also speedkilling them on sections where time-based bonus enemies are spawned) and to keep the chain going for the entire stage. While many sections of the game can be chained intuitively, some others are quite tricky to chain properly, requiring methodic planning and experimentation to come up with good strategies. In general, a thoughtful approach is rewarded at any skill level, and picking which enemies to add to the chain and which ones to let go should yield better results than improvising a full chain of a section or just carelessly blasting around
- Boss time bonus: during boss battles there’s a timer which goes down as time passes (starting from 100 seconds for main bosses) and stops when the boss is defeated - each remaining second is worth ten thousands points, therefore speedkilling is rewarded. Some mid-bosses also give a time bonus, but the timer starts from a lower number (if the main boss is not killed afterwards, the time bonus that was racked up is lost). In 2P mode, the boss time bonus is assigned in full to both players
- Extend bonus: Each life that is in stock at the end of the game is worth half a million points. The player’s life stock starts with two lives by default (game is over if you die three times) and extra lives can be gained by scoring (the first one after three million points and the others after every five million, with the standard extend conditions)
- Bullet eating: absorbing a single bullet gives 100 points, while sitting on a laser beam yields 100 points per frame (the rare homing shots fired off by some enemies are worth either 500 or 1000 points). While this is a scoring element that is often neglected, absorbing bullets and lasers to the fullest extent possible can make the difference between very advanced players, when the enemy chaining has been mostly perfected
- Damaging enemies: an enemy hit is generally worth 20 points (40 points for hits on opposite polarity enemies). Score increments of 10 points are also possible, but rarer. A single homing laser hit gives 100 points (again, 200 for opposite polarity), unless the enemy can take less than five single-shot hits, in which case it is worth how many it can take times 20 (e.g. if the enemy can take three hits, it is worth 60 points). This is by far the least important scoring element, and the player also has limited to no degree of control over it (since the hit value is fixed, and chaining requires to kill as many enemies as possible anyway). Still, it is possible to go after a purely hit-based score increase during the few idle moments on some main boss fights, by targeting secondary pods or hatches
The player’s scoring performance is graded at the end of each stage, with ranks going from C to S++. The thresholds are fixed across all the various modes and difficulties. They are shown below in millions, starting from the B rank (C+ and C++ omitted):
Save for possibly the final chapter on arcade easy, the S++ rank can be achieved on every stage of every mode; in fact, in most cases it is possible to score way higher than what it takes to get an S++. Definitely, for the most dedicated players getting an S++ is only where things get serious…
Ikaruga has five stages, with a full run through the game taking about 25 minutes (the game doesn’t loop). Every stage features an introductory sequence displaying the chapter’s title and a short blurb and ends with a boss fight, but aside for this the stages can vary significantly (actually, even the introductory sequence itself occurs only around mid-stage in stage 3 and 5). Chapter 1 and 2 do not have any mid-boss, while chapter 3 has one (with no time bonus awarded for its defeat) and chapter 4 has two (both giving a time bonus instead). Chapter 3 is riddled with environmental hazards, while they play a minor role in most other stages. The last stage is unique for ending with a boss rush, then giving way to the final boss of the game - the Stone-Like.
|Chapter 1: Ideal |
After hearing about the unique capabilities of the Ikaruga, Hourai Tenro ordered an expeditionary force under general Asami to destroy the aircraft while stationed inside its launching carrier, the Sword of Acala, but Shinra and his fellows were ready for a counterattack. Village elder Kazamori breaks the silence with some lines from an old poem: “I won't give up even if my Ideal isn't fulfilled. My will, just as my regrets, won't ever end. My comrades... it is time"
|Chapter 2: Trial
The battlefield is the country of Agi, which fell under Hourai’s control after the ‘Buppousou’ Butsutekkai started targeting the civilians, forcing Agi’s leader to surrender and Shinra and his comrades to retreat. Going on a mission that will for sure be a Trial of his abilities, Shinra carries out a surprise attack on the occupation forces and infiltrates the military facility that is being built underground by the enemy's troops..
|Chapter 3: Faith |
After liberating the country of Agi, a war of attrition ensues, which in the long term would lead to Hourai’s victory. To end the stalemate, Shinra is planning to launch a direct assault by crossing the border to the country of Hourai, but a fortified ravine, considered impenetrable for its environmental hazards, stands in the way. After seeing Shinra’s Faith in the plan, engineer Amanai overcomes his hesitations and prepares the Ikaruga for departure..
|Chapter 4: Reality
After clearing the ravine, Shinra faces the bulk of the Hourai army led by general Kira from his giant ‘Misago’ Butsutekkai. Shinra and his comrades opt for a methodical combat strategy, attacking the weak spots of the Butsutekkai one by one. They eventually succeed, but the strenuous fight took its toll on Shinra, as the Ikaruga interfaces directly with the pilot’s neural system, accelerating the death of human nerve cells. Shinra must now confront a harsh Reality: the extreme mental drain due to piloting the Ikaruga will surely exact a hefty price..
|Final Chapter: Metempsychosis |
Unfazed by the thought that his time may draw near, Shinra bursts into Hourai’s headquarters for the final battle. After taking down the last few enemies, he faces the mighty ‘Tageri’ Butsutekkai. Hourai tries to divert his resolve with words to no avail - Shinra keeps fighting with his last drops of strenght and in the heat of the battle he also hears the voices of two spiritual beings that appeared in his dreams. And then, right after he manages to destroy Hourai Tenro’s flagship, the Stone-Like emerges from the debris..
|Epilogue: The Stone-Like
After convincing the engineer to deactivate the restraining devices of the Ikaruga, Shinra unleashes all the energy stored onboard, and meets his destiny just a moment before he can witness the Stone-Like explode. As his soul Transmigrates, the two spiritual beings of his dreams manifest themselves..
Shinra: "Was that… the right thing to do?"
|Version||Physical||Tate option||Prototype mode||Practice mode||Online features||Extras section||Energy Bar Layout||Chain Count||Translations||Port fidelity||Misc|
|Yes, JP only||Yes, no yoko||No||No, Trial mode only (first two stages w/ unlimited lives)||No||No||Horizontal only||No||-||-||Runs the same on NAOMI 1 and NAOMI 2|
|Yes, JP only||Yes||Yes||Yes, stage select||No||Yes||Both (based on yoko/tate)||Yes (on VMU)||-||Highest||Only port w/ slowdowns (more faithful on tate)|
|Yes, JP-US-EU||Yes||Yes||Yes, stage and section select (Conquest mode)||Dedicated website w/ leaderboards (no longer supported)||Yes||Both (based on yoko/tate)||Yes (press Z button)||No 1||JP-US: High
EU: Low (50Hz, interlaced only, Ch1 boss inaccuracy 2)
|Demo videos and slow motion practice on Conquest mode|
|No||Yes||Yes||Yes, stage select||Yes (leaderboards, replay download, 2P co-op)||No||Both (user choice)||Yes||Yes (partial)||Lowest (several inaccuracies 3)||HD graphics and achievements *|
|No||Yes||Yes||Yes, stage select||??||??||??||Yes||-||High 4||Short cutscene on Ch1 and final boss fights *|
|No||Yes||Yes||Yes, stage select 5||Yes (leaderboards, replay download)||Yes||Both (user choice)||Yes||Yes (partial)||High 6||Additional graphic options *|
|Yes, JP-US (2020)||Yes||Yes||Yes, stage select 5||Yes (leaderboards, replay download)||Yes||Both (user choice)||Yes||Yes (partial)||High 6||Supports 4K on PS4 Pro|
- The GameCube version completely omitted almost all of the text from the in-game stage transitions and Extras menus rather than translate it. The Extras images with character and story information were simply left blank (and this change has been carried over to newer ports, unfortunately). However, for later ports after the GameCube release the story text during gameplay and stage transitions was fully translated 
- On the last phase of the boss, the energy release hits the pods on the sides instead of the boss, which makes it impossible to finish the battle as quickly as on other versions
- Known main differences are: Ch2 boss can be damaged before hatches are closed, Ch3 mid-boss orbiting pods spin the opposite way, Ch3 bonus enemies pattern is altered making them much easier to chain, Ch5 massive enemies (chougenbou) at the end of the first section cannot be approached up close thus precluding optimal scoring on it
- Based on the few gameplay videos available. According to the japanese Wikipedia voice of the game, in its latest build the NESiCA version could be described as a "Steam version [playable] on a NESiCA system"
- Stone-Like (final boss) not playable on Practice mode. No restart option on this mode (or any other mode)
- There are several minor differences with respect to the arcade version, all of them mostly inconsequential
* Feature(s) shared by the following versions
All of the ships and bosses of Ikaruga are named after birds in the japanese language (the final boss is the only exception). As for the player's ships, ‘ikaruga’ - or generally, just ‘ikaru’ (イカル) - refers to the japanese grosbeak (a flock of which can be seen flying around during the game's end credits), while 'ginkei' (ギンケイ) is a species of pheasant. Down below are images of all named enemies and bosses, with a link to the corresponding bird:
Ikaruga contains several buddhist references , of which some are listed here:
- ‘Ikaruga’ (斑鳩町) is also the name of a town in the prefecture of Nara, where Buddhism was first introduced in Japan;
- the carrier from where the Ikaruga is launched at the start of the game is called ‘Sword of Acala’, where ‘Acala’ refers to one of the buddhist kings of wisdom;
- the second chapter’s boss name, ‘Buppousou’ (仏法僧), is another name for the Buddha, its teachings, and the monastic order of Buddhism (also known as the Three Jewels). This boss is also notable for having a yin-and-yang symbol carved on its main body
- the fifth chapter of the game is titled ‘Metempsychosis’, which is a greek term referring to the transmigration of the soul, a central buddhist tenet. While all the chapter’s titles are linked to events related to the game’s story, some have taken them to represent the path towards enlightenment followed by the main character (or even the player) in the game
The full name of Ikaruga’s final boss is ‘Ubusunagami Oukinokai’ (産土神黄輝ノ塊, roughly translated as ‘Golden-Glowing Rock of the Stone-Like God’  though ‘Ubusunagami’ is more accurately translated as ‘Birthplace Deity’). It is clearly the same final boss as that of Radiant Silvergun, the ‘Stone-Like object’. In RSG the Stone-Like is the Earth ‘Guardian’, which judges mankind to unfathomable standards: once humanity derails too much from them, it will reset the world, wiping out all humans and allowing some clones to start populating the Earth again, in an endless loop. In Ikaruga, the Ubusunagami Oukinokai does not have any characterization, and while some believe it to have the same role as in RSG, others think that in this case it is entirely controlled and exploited by humans, in accordance with the game's story (and so driving more convincingly its main theme, involving the very human struggle of reaching a peaceful coexistence thanks to mutual understanding)
For the GameCube release of the game, the publisher (Infogrames, under the Atari label) launched a scoring competition, the ‘Ikaruga Net Ranking Contest’, in the form of a dedicated website where players from all over the world could submit their scores on either arcade or prototype mode on normal difficulty (1P only). It was one of the first instances of official online scoreboards for a shooting game. The players with the five highest scores on each mode at the closure of the contest were awarded an official Atari trophy. The legitimacy of the scores was ensured by the fact that the GC version had a dedicated ‘Challenge’ mode, which at the end of the run displayed a twelve-character code that uniquely represented the score achieved and that was to be entered on the website in order to submit the actual score. After the official website went down, a few dedicated players managed to crack the code and implemented the feature on unofficial scoreboards hosted on the ‘ikaruga.co.uk’ website, which remained the point of reference for the western community of Ikaruga for several years
Notes and references
- Treasure's founder Masato Maegawa Interview
- Game director Hiroshi Iuchi Interview
- A japanese transcript of the 'Prologue' text file and of the writings on the sound test can be found here,
while an english translation is available on the ‘Extras’ section of PBSaffran’s comprehensive guide to the game
- An alternative translation for the stage transitions is available on this image, while transcripts can be found here
- Announcement of the Dreamcast version and interview for the release (japanese only)
- Announcement of the Steam version and interview for the release (japanese only)
- Eboshidori is shown in-game with a damaged helmet, which is a hint of its previous battle with Shinra
- Misago's bottom part (not visible in the image) is modelled after Rafflesia flowers
- See the relevant article on this archived Ikaruga fan site
- The trailer for the ‘Ikaruga Appreciate DVD’ can be watched here
Original article written by XER, MAZ, powerfuran