Ikaruga

Ikaruga (斑鳩) is a vertical-scrolling shmup 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, with the player’s ship being able to switch between the two colours. When asked about the inspiration for this game mechanic, game director Hiroshi Iuchi spoke 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 it has been ported to multiple home consoles (Sega Dreamcast, Nintendo GameCube and Switch, Xbox 360, PlayStation 4) and online platforms (NESiCAxLive and Steam), with varying features and fidelity to the original version.

In general, Ikaruga is considered to be a very methodical shooting game. It discourages an improvised playing style, instead placing emphasis on rigorous routing and execution at any level of play.

Story
The storyline of Ikaruga is only hinted at in-game and is fleshed out on some of the ported versions (as unlockable bonus features ).

This is the prologue to 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 just one member survived, the strong-willed Shinra [Player 1]. Refusing to call it quits, Shinra built a makeshift aircraft (‘Shirasagi’) and took off on a lone sortie against Hourai’s forces. He managed to make his way through the enemy troops 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 inhabited by exiled people - the Village of the Grosbeak (‘Ikaruga no Sato’). He was recovered from the wreckage and nursed back to health. Unwilling to live with regret, Shinra renewed his pledge to defeat Hourai, which prompted the villagers to equip him with a technological marvel - the only aircraft capable of switching polarity and absorbing bullets, built by former engineering genius Amanai and bearing the village’s name: Ikaruga. Thanks to the unique features of his new ship, Shinra was then able to fight general Asami’s Butsutekkai on equal terms, blocking his foray on the village and driving him away. Soon after, Shinra finds a comrade in Kagari [Player 2], a pilot of incredible resistance who originally fought for Hourai but changed side in the pursuit of freedom. A woman with a strong character, Kagari convinced Amanai to upgrade her ship, the Ginkei, to the same capabilities as the Ikaruga. After a brief training period with their unique ships, the day comes for the two pilots to set off and confront Hourai Tenro’s forces...

Gameplay Overview
The gameplay of Ikaruga revolves around the black and white polarity system, which entails the following:
 * the enemy's bullets are either black or white, with the player’s ship being able to switch between the two polarities: bullets of the opposite colour will destroy it, while those of the same colour will be absorbed (and charge up the Energy Bar)
 * enemies are also black or white, suffering double damage when hit by opposite-polarity fire and releasing revenge bullets of their own colour once destroyed (depending on the game’s difficulty mode)
 * enemies killed in sets of three of the same colour make a chain, which yields a varying amount of points up to a maximum value (‘Max Chain’)

In order to advance in the game, one has to get accustomed with switching polarity back and forth according to on-screen bullets, revenge bullets (if any) and, eventually, the polarity of the enemies (in order to deal more damage). Although the ship has a small hitbox - which is a frequent characteristic of bullet-hell games - Ikaruga isn't generally associated with this sub-genre, often requiring mastery of the polarity system rather than bullet-dodging skills. The game also presents navigational challenges where the player must steer away from enemies and environmental hazards. In some sections, speedkilling specific sets of enemies can trigger 'bonus' ones to spawn, which potentially allows for more chains. There are no power-ups or items, nor a rank system (although losing a life in some sections causes them to get toned down a bit).

Controls
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.

Single Shot
Tapping the fire button will fire off a single shot. This shot type is used in order to take down specific enemies, which is often needed for chaining. A single shot deals a damage of 2HP to enemies of the same polarity (4HP if opposite) and can hit multiple enemies if they are close together.

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, since it has the same power as the double-shot but concentrated on a smaller area.

Double Shot
Holding the fire button down will fire off a double-shot stream. This is the main shot type of the game. Like for single shots, a double-shot as a whole deals a damage of 2HP to enemies of the same polarity (4HP if opposite) and can hit multiple enemies if close together. The double-shot is made up of two independent projectiles: each can deal a damage of 1HP or 2HP to different enemies (based on polarity). In fact, when a double-shot hits a 2HP enemy of opposite polarity, only one projectile disappears (as opposed to both for an enemy of the same polarity), with the other carrying on forward - this is the reason why even clusters of popcorn enemies are destroyed more quickly when shooting with the opposite polarity.

Since popcorn enemies have a minimum of 2HP, it follows that half of a double-shot is not enough to take down an undamaged enemy of the same polarity (this can be relevant when firing while shifting to one side, since the bullet skewing tends to disperse the firepower).

Another tidbit worth noting is that 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). This can be exploited during Boss fights or when firing to durable enemies.

Energy Release
When the Energy Bar is at least partially charged, pressing the relevant button(s) 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 Energy Bar (it is made up of twelve blocks, each one representing a laser and taking ten bullets to charge up). One laser inflicts as much damage as five single shots (i.e. 10HP to enemies of its own polarity). While the Energy release is generally efficient in terms of pursuing different targets and/or concentrating more damage on stronger foes, it is not a panic bomb: it does not necessarily 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 which is useful for dealing with large enemies or Bosses and, at higher levels of play, for racking up chains quickly. Since the lasers have no regard for chain integrity, in order to preserve it through an Energy release, players typically use it on clusters of enemies of the same polarity - however, it is also possible to chain both black and white enemies with a single release.

These are the main points underpinning the Energy release mechanic:
 * the lasers are ejected stacked one on top of the other on each side of the ship (six on the left and six on the right for a full release) and their different placement has some bearing on their behaviour (for example, the upper lasers depart a bit earlier than the others and tend to hit their target only after turning around on their path)
 * assuming on-screen enemies of equal durability, the lasers select their target based essentially on their proximity to the position of the release and the preferred path / screen-time of each laser in the given volley. In general, when a full release is launched amid spaced-out enemies, those that are immediately below or beside the ship will be taken down first, followed by the ones that are in front and finally those farther below
 * the lasers fly at a varying speed: they are slower when turning around and faster when going straight.

It must be stressed that when the chain is preserved through a release on black and white enemies, it is only as a by-product of the lasers' fixed behaviour, which as per description above is irrespective of the enemies' colour and is based on deterministic factors such as timing, position, number of lasers - there are no random elements to it, therefore once figured out that a release can be successfully used in a given section, its behaviour will stay consistent if the original conditions are replicated closely enough. On the other hand, very slight alterations can change the outcome of the release considerably.



Difficulty Modes
Ikaruga has three difficulty modes. The basic gameplay difference lies in the revenge bullets which are released when enemies are destroyed:
 * Easy: enemies never release revenge bullets
 * Normal: enemies of the same polarity as the last hit release revenge bullets. The number of revenge bullets depends on the enemy - the larger and more durable it is, the more bullets are released
 * Hard: enemies always release revenge bullets. Enemies of the same polarity as the last hit release the same number of bullets as on Normal; enemies of the opposite polarity to the last hit release half the number of bullets (which are also slower in speed).

There are also changes to some of the enemies' patterns and attacks, bullet patterns and Boss fights. With respect to Normal mode:
 * on Easy, there may be less enemies in some sections (Chapter 3 and 4); enemies may shoot less bullets; bullet patterns may be different (Chapter 2); the Bosses may have less HP (Chapter 4 and 5) and their attacks may pose less of a threat (all Chapters)
 * on Hard, enemies may shoot more bullets; the Bosses' attacks may pose more of a threat (all Chapters).

More details about some of these changes are provided in the Enemies and Bosses sections.

As a result of these differences, optimal strategies and scoring potential can change considerably across the various difficulties.

Prototype Mode
Beside the standard Arcade mode, 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 replaces the Energy Bar with an Energy stock, represented by a counter which can go up to 999. The stock is depleted by using the main shots (unlike on Arcade) or releasing Energy. Both of the main shot types take up 2 ammos each and Energy lasers require 10 ammos each (a full release is still twelve lasers i.e. 120 ammos). The initial stock depends on the difficulty (500 on Easy, 300 on Normal, 100 on Hard) and is replenished by absorbing bullets. Each absorbed bullet is worth 3 ammos, while sitting on a laser beam provides 3 ammos per frame. If the reserves are depleted, the ship can only inflict damage by point-blanking the enemies.

The implications of these changes vary depending on the difficulty mode:


 * on Normal and Hard modes, the presence of revenge bullets easily guarantees large reserves of ammos and the limited Energy stock is not a real constraint. Actually, the opposite is true - since the stock can hold up to eight full releases, it is possible to launch multiple of them one after the other (unlike on Arcade mode, where the Energy Bar maxes out at one). The increased firepower is such that it can make fodder out of Main Bosses, and also allows for easier speedkills of standard enemies and generally more chaining opportunities (although the different Energy release mechanic sometimes makes it impossible to use in sections where optimal chaining requires small releases)


 * on Easy mode, owing to the lack of revenge bullets, it is instead very frequent to run on low or even no reserves. This requires tailored strategies and a different play style altogether, where the stock must be rationed efficiently and point-blank shooting is often needed.

As a result of these factors, the scoring potential on Prototype mode is higher than on the corresponding difficulty on Arcade mode - considerably so on Normal and Hard, less so on Easy.

Others
Ikaruga can also be played on 2P mode. The two ships differ only visually and of course cannot overlap (otherwise they would be invulnerable to both white and black bullets while on different polarities). Gameplay-wise, there are no differences with respect to 1P mode with the exception of the first two Bosses having more HP. The scoring potential is much higher on 2P mode, due to the increased chaining and bullet eating opportunities on top of the higher Boss time bonus (assigned in full to both players) and Extend bonus which can be accomplished. Some versions allow for cooperative gaming over the internet or have an option for double-play with a single controller (for players that rise to the challenge of controlling both ships solo).

It must also be noted that, while not representing a different mode, it is possible to finish the entire game on a single life without ever firing a bullet (on any actual game mode). The pacifist player receives a ‘Dot Eater’ rank on the stage breakdown.

Score system
For world record scores, please refer to the Hall of Records entry

Scoring in Ikaruga is mostly centered around chaining enemies based on their polarity, but there are a few other scoring elements in the game. They are all presented here, in order of importance:
 * Chaining: taking down three enemies of the same polarity in a row makes a chain. Each following chain can be of the same or of 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 sets of three of the same colour. 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). The first chains give 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). For every chain worth 25600 points, a robotic voice can be heard uttering either ‘Max Chain’, ‘Excellent’ or ‘Splendid’. The chain is broken when the player fails to kill enemies in triples of the same colour or dies, and resets at the start of each stage. A max chain break costs a minimum of 204900 points (25600+204800-25500, i.e. chain dropped + 8 missed max chains - first 8 chains), assuming that another chain is restarted immediately after and no further enemy triples are missed out (which is almost never the case). It follows that, in order to score more points, as many enemies as possible must be chained (which also implies going for quick kills in sections where time-based bonus enemies are spawned) and that the chain should be kept going for the entire stage. There are very few sections where anything other than elementary chaining can be left to improvisation - the game very much requires predetermined strategies to come up with good scores. These can of course be of a varying complexity, but even basic routes tend to give better results than on-the-fly chaining
 * Boss time bonus: during Boss fights there is a countdown timer (generally starting from 100 seconds) which stops when the Boss is defeated. Each remaining second is worth 10000 points, thus rewarding speedkills. Some Mid-bosses also give a time bonus (but if the Main Boss is not killed afterwards, the mid-boss bonus will be lost)
 * 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 after dying three times) and extra lives can be gained by scoring (the first one after reaching 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 uncommon homing shots fired off by some enemies are worth 500/1000 points). While this is a scoring element that is often neglected, absorbing bullets and lasers to the fullest extent possible can make the difference at high levels of play, once chaining has been mostly optimized
 * Damaging enemies: killing or simply damaging enemies gives a small amount of points. Every HP removed is worth 10 points (though such a small increment rarely happens given that single shots and whole double-shots both take off at least 2HP from enemies). This is by far the least important scoring element and the player also has limited to no degree of control over it (since the enemies' HP are fixed, and chaining requires killing as many enemies as possible anyway). Still, it is possible to go after small hit-based score increments on the few idle moments during some Main Boss fights, by firing at supporting pods or protective covers.

Other than by extending the life stock, scoring does not affect the chance of survival/1CC in Ikaruga (as opposed to its ‘spiritual prequel’ Radiant Silvergun, which features upgradable weapons based on score). Still, the chaining mechanism is not simply a complement to the polarity system but very much a defining element of the game, which accounts for its peculiar enemy patterns and behaviours (enemies are often passive or even suicidal, and were also arranged so that it would be extremely difficult to tell what the “correct” path was for scoring ).

The player’s scoring performance is graded at the end of each stage, with ranks going from C to S++. Although the scoring potential varies considerably across modes and difficulties, the ranking thresholds are fixed. Except perhaps for the Final Chapter on Arcade Easy, the S++ rank can be achieved on every stage of every mode (in fact, it is often possible to score way higher than what it takes to get S++).

The table below shows, for each stage, the ranking thresholds in millions (C+ and C++ ranks omitted) and, for each difficulty on Arcade and Prototype modes (1P), the known (accomplished) max chains (please note that these two pieces of information are not related in any way and are presented on the same table only for formatting reasons).

* Additional chain(s) known to be possible based on existing strategies

Stages
Ikaruga has five stages (referred to as Chapters), with a full run through the game taking up about 25 minutes. Every stage features a short cutscene which displays the Chapter’s title and some related text and ends with a Boss fight, but they tend to vary significantly otherwise. To give some examples: Chapter 1 and 2 do not have a Mid-boss, while Chapter 3 has one and Chapter 4 has two; Chapter 3 is riddled with environmental hazards, while they play a minor role in most other stages; the Final Chapter is unique for ending with a Boss rush, then giving place to the Final Boss of the game - the Stone-Like.

The Chapters are presented below with the associated plot elements :

Enemies
Most of the enemies and ships in Ikaruga are given names adapted from bird species (the few that do not fly have generic names). It is not uncommon for enemies in the game to pose only a mild threat (sometimes being just a collision hazard), with the actual challenge represented by chaining them instead. The enemies are listed below in order of appearance, along with HP and revenge bullet information. As a reference, the damage dealt by a single shot is 2-4HP and the one dealt by a full Energy release is 120-240HP (respectively, to enemies of the same and of opposite polarity).

Quick Reference Table
Enemies First Encountered in Chapter 1

Enemies First Encountered in Chapter 2

Enemies First Encountered in Chapter 3

Enemies First Encountered in Chapter 4 *

Enemies First Encountered in Chapter 5


 * Enemies that are encountered as Chapter 4 Mid-bosses are described in the Boss section
 * As noted among the version differences, in the Xbox 360 version of the game the Chougenbou have larger collision boxes, which prevents optimal absorption and ultimately reduces the scoring potential of the Chapter

Bosses
Introduced by a warning sign at the end of each stage, the Main Bosses of Ikaruga are also named after bird species and are generically known as ‘Butsutekkai’ (仏鉄塊), which roughly translates to ‘iron Buddha’. The bosses are manned by enemy officials and generally pose multiple threats with their various attacks. They are often made of several parts to be destroyed or hit. These do not provide chains, with the exception of the few existing Mid-bosses - basically the two encountered on Chapter 4, which are the only ones that are embedded on the body of the Main Boss (Shigi is a unique, independent Mid-boss and the first two Bosses of the Final Chapter generally are not considered to be Mid-bosses, nor provide chains).

Down below is a table showing the Bosses' HP (which can vary with the game modes), followed by a profile for each one with some basic facts and a description. The Max Time Bonus numbers are based on the known best times accomplished on 1P Arcade mode (contingent on a specified Energy Bar status when entering the fight - if unspecified, the given time can be accomplished with an empty Bar). Unless otherwise noted in the description, the time limit for the Boss fights is 100 seconds.

Strategy
Please refer to the Video index

Version differences
1. If featured, generally has to be unlocked on a per stage, per difficulty basis (the requirement is getting to the given stage without using continues) 2. If present, generally have to be unlocked by fulfilling certain scoring or time requirements. They essentially consist in galleries and soundtracks. The relative game menu label can vary (for example, it is ‘Appendix’ on the DC and Steam versions and ‘Extras’ on the GC version) 3. Also include four wallpapers and a ‘Prologue’ text file which further expands on the game's backstory (in japanese)     (can be accessed by inserting the gd-rom into a computer disc drive) 4. 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). However, for later ports after the GameCube release the story text during gameplay and stage transitions was fully translated (with mixed results) 5. On the last phase of the Boss, the Energy release targets the supporting pods instead of the Boss, which makes the optimal strategy non-viable 6. Known main differences are: the Chapter 2 Boss can be damaged before covers are closed, the Rotating Bits of Shigi spin the opposite way,     Chapter 3 bonus enemies' pattern is altered making them much easier to chain, the Chougenbou (massive enemies found on the Final Chapter)      cannot be approached up close thus precluding optimal absorption and scoring 7. Based on the few gameplay videos available. According to the japanese Wikipedia article on the game, after the latest patches the NESiCA version     can be described as a "Steam version playable on a NESiCA system" 8. Stone-Like (Final Boss) not playable on Practice mode. No restart option on this mode (or any other mode) 9. There are several minor differences with respect to the Arcade version, all of them mostly inconsequential * Feature(s) shared by later versions. Related differences: The game's resolution is up to 720p on the Xbox 360, up to 1080p on Switch and up to 4K on Steam and PS4 Pro There are 12 achievements on the Xbox 360 and 25 achievements on the Steam, PS4 and Switch versions The Steam version has additional ‘Quality’ settings (AA, texture filtering, pixel lighting). This video shows the settings in common

Trivia
Ikaruga contains several buddhist references. Some were pointed out in the above sections - the other ones are listed below:
 * ‘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;
 * Warning_message_text.png the Boss warning that appears at the end of each Chapter bears a passage in Sanskrit written in Siddham script, which represents a spell that grants safety from dangerous situations (the same Siddham characters also appear on the control device fitted on the Stone-Like)
 * the name of the Chapter 2 Boss, ‘Buppousou’ (仏法僧), also stands for the Buddha, its teachings, and the monastic order of Buddhism (known as the Three Jewels). This Boss is also notable for having a yin-and-yang symbol carved on its main body
 * the Final 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 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 Stone of the 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's ‘guardian’, which judges mankind to unfathomable standards: once humanity derails too much from them, it resets the world, wiping out everyone and allowing some human clones to start populating the earth again, in an endless loop. In Ikaruga, the Final Boss does not have any characterization, and while some believe it to have the same role as in its prequel, others think that it is entirely controlled and exploited by humans, in accordance with the game's main theme (which is about the entirely human struggle of reaching a peaceful coexistence through mutual understanding).

An official demonstration video disc titled ‘Ikaruga Appreciate DVD’ was published by Treasure in April 2003, showcasing advanced scoring strategies for each difficulty mode.



Following the GameCube release of the game, a scoring competition was launched by the publisher (Infogrames, under the Atari label). Known as the ‘Ikaruga Net Ranking’ contest, it ran for about three months, during which players from all over the world could submit scores to a dedicated website. The legitimacy of the scores was ensured by the inclusion of a dedicated ‘Challenge’ mode on the GC version, which assigned a unique 12-digit code to every score achieved (on 1P Normal Arcade and Prototype modes): this code had to be entered on the website for the score to be submitted. The players with the five highest scores on each mode at the end of the contest received an official Atari trophy. 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
Article written by XER, MAZ, Softdrink, Plasmo, powerfuran