Viper Phase 1

Viper Phase 1

Title screen

Developer:	Seibu Kaihatsu
Music:	Go Sato
Program:	Yoritaka Kasai
Art:	Toshinobu Komazawa
Release date:	Japan Old Version: May 1995 Japan New Version: August 1995 USA: October 1995
Previous game:	Raiden DX
Next game:	Raiden Fighters

Viper Phase 1 (バイパーフェイズ1) is a 1995 vertically scrolling shooter arcade video game developed and published by Seibu Kaihatsu. Often regarded as a spin-off or spiritual successor to the Raiden series, the game shares many similarities in terms of gameplay mechanics and design philosophy. Viper Phase 1 is the first game developed for Seibu Kaihatsu's SPI system board, featuring detailed sprite-based graphics and elaborate explosion effects.

The initial release (now known unofficially as Old Version) failed to gain acceptance among many players due to its unorthodox weapons system. Three months later, a revised Viper Phase 1 New Version was released, featuring adjustments that brought the gameplay closer to Raiden, such as making sub-weapons permanent (see Version Differences). This version also formed the basis for overseas releases of Viper Phase 1.

Hamster Corporation released the game (featuring both versions) as part of their Arcade Archives series for the Nintendo Switch and Sony PlayStation 4 in December 2024.

For replay videos, visit the Video Index.

Gameplay Overview

The game consists of eight stages and supports two-player simultaneous play. There are no extends.

Controls

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• 8-way joystick: Moves the player's craft. As in the Raiden series, diagonal movement is faster than strictly vertical or horizontal movement (with vertical movement being slower than horizontal movement).
• A: Simultaneously fires the player's main weapon and sub-weapon.
• B: Activates the player's bomb. There is a slight delay before the bomb detonates.

Weapons

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Sub-weapons can be equipped by destroying a weapon carrier craft and picking up the weapon change item it drops. Weapon carriers generally appear in sync with specific enemy ships during the stages and can also appear during boss battles. Weapon change items float down the screen oscillating right and left and changing their weapon type every time they change direction. The starting weapon type is random, but the cycle order is fixed as Wide, Laser, Missile, Napalm, Wide, Laser... and so on.

Icon	Name	Function
	Wide	Fires shots in a fan-shaped pattern covering a wide area. Powering up expands the firing range. While the damage per individual shot is low, point-blanking enemies unleashes devastating attack power.
	Laser	Fires a laser beam straight ahead. Although the effective range is narrow, the weapon is powerful. Powering up increases the thickness of the beam. This weapon is effective against heavily armored enemies.
	Missile	Launches missiles across a wide area in front of your ship. The missiles travel slowly but explode upon impact, dealing massive damage. Powering up increases the number of missiles fired and expands the size of the resulting explosions.
	Napalm	Fires missiles straight ahead from both wings of your ship. They detonate upon impact, dealing concentrated, high-damage hits. Powering up increases the number of explosions generated by each missile, allowing the blast to cover a wider area.

Items

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Destroying item carriers that appear at predetermined points throughout each stage will release either a power-up item or a bomb item. These items appear in a repeating power-up, power-up, bomb, power-up, power-up, bomb... sequence with every item carrier destroyed.

Medals can be revealed by destroying various airborne and ground-based targets.

Icon	Name	Function
	Power-up	Upgrades both the main weapon and sub-weapon shot power up to a maximum of three levels. However, if you choose the Laser or Napalm sub-weapon, your main shot is downgraded to its weakest form. In Old Version only the main weapon is upgraded.
	Bomb	Increases the player bomb stock by 1.
	Small medal	Worth 500 points, or 2,000 points at max value.
	Large medal	Worth 1,000 points, or 3,000 points at max value.
	Special medal	Worth 30,000 points, or 100,000 points at max value. Can be revealed twice in the game.

Rank

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In Viper Phase 1 rank is chiefly a survival timer. As you stay alive, rank gradually climbs toward its maximum. Dying lowers rank—normally by 2 levels in single-player on default settings and delays the next increase. The rate is determined by the current stage and DIP difficulty.

Higher rank:

• allows more enemy bullets on screen;
• changes when enemies are permitted to shoot;
• shortens enemy timers;
• increases enemy bullet speed;
• activates harder behavior in numerous enemy-specific scripts.

Power level doesn't raise rank, but it adds a small amount to the separate bullet-speed difficulty calculation.

Loops

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A second loop is present in Viper Phase 1 USA. All other versions are single-loop.

Endings

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There are two narrative outcomes determined by whether you stop the planet-destroying missile in Stage 8. Depending on the ending reached a different completion bonus is awarded.

Scoring

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This section refers primarily to the New Version of the game.

Ground Medals

At regular intervals ground medals will have a brief moment where they stop shimmering. Collecting them at that exact moment awards the maximum value of 2,000 points or 3,000 points, respectively, for small and large medals, as well as 100,000 points for a special medal.

Airborne Medals

Airborne medals do not feature a shimmering animation and will always be worth the base value of 500 points or 1,000 points, respectively, for small and large medals.

In most cases, airborne medals will be released by specific bonus pod enemies. These enemies appear at a random horizontal position and at fixed times for each stage based on the elapsed time from the start of the stage. They will descend straight down from the top of the screen, briefly pause when they reach their inflection point near the center, and then change their trajectory back up and off the screen. Destroying a bonus pod on the way down yields five medals, but destroying it only after it has begun to travel back up the screen will make it drop ten medals. The ratio between small and large medals that are dropped is random.

Stage Clear Bonus

At the end of each stage, the game awards a bonus based on enemies destroyed, medals collected, bombs remaining, and the destruction rate:

stage clear bonus = (enemies destroyed × 10 + bombs × 300 + medals × 100) × destruction-rate multiplier

The destruction multiplier is determined by the percentage of enemies destroyed. For single-player, the destruction-rate multiplier is as follows:

Percent Destroyed	Multiplier
0–79%	x10
80–89%	x20
90–94%	x30
95–98%	x40
99%	x50
100%	x100

There is no rounding to the nearest integer. So if the actual ratio is 98.99%, the game treats that as 98% → ×40, not 99% → ×50.

This makes a 100% destruction rate particularly valuable: the multiplier jumps from ×50 at 99% to ×100 at 100%, effectively doubling the entire stage clear bonus.

Two-Player Exception

In simultaneous two-player play, the multiplier table is slightly different:

Percent Destroyed	Multiplier
0–79%	x10
80–89%	x20
90–94%	x30
95–99%	x40
100%	x50

Stage 4 Bug

Due to incorrect spawn coordinates, several enemies in Stage 4 are immediately deleted before the player can destroy them. As a result, a 100% destruction rate cannot legitimately be achieved in Stage 4 and 99% is the maximum. The Old Version has an equivalent bug in Stage 6.

All Clear Bonus

After completing the game, an additional bonus is awarded based on final-mission success, total enemies destroyed, total medals collected, bombs used, and deaths.

all clear bonus = completion bonus + (total enemies × 100) + (total medals × 1,000) + bomb bonus + survival bonus

Completion Bonus

If the missile in the final mission stopped, thereby achieving the good ending, 1,000,000 points are awarded. If the player fails to do so only 100,000 points are awarded.

Bomb Bonus

The Bomb Bonus is based on the total number of bombs used during the entire game:

Bombs used	Bonus
0	500,000
1	300,000
2	100,000
3	50,000
4	40,000
5	30,000
6	20,000
7	10,000
8	9,000
9	8,000
10	7,000
11	6,000
12	5,000
13	4,000
14	3,000
15+	2,000

Survival Bonus

The Survival Bonus is based on the total number of deaths during the entire game:

Deaths	Bonus
0	500,000
1	400,000
2	300,000

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Strategy

This section refers primarily to the New Version of the game.

Basic Strategy

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• Wide shot is by far the most viable sub-weapon for the entirety of the game due to its powerful point-blanking ability.
• Using external 30Hz rapid-fire is highly recommended.
• Due to the slight delay between activation and detonation, bombs should be used offensively and at pre-planned points in the game.
• When playing for score, prioritize achieving a 100% enemy destruction rate and a clearing the game using as few lives and bombs as possible, as this will have the greatest effect on score.
• Use screen sealing to your advantage: moving to the far right or left side of the screen so that enemies on the opposite side are no longer visible onscreen will prevent them from firing shots.

Enemy Spawn Behavior

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Viper Phase 1 uses both fixed and dynamic enemy spawning. Fixed enemies are tied to specific stage scroll positions and therefore normally appear at the same place on every run. Other, primarily airborne enemies belong to sequential wave lists whose timing depends partly on how quickly the previous wave is cleared. The game keeps a counter of active wave enemies; when it reaches zero, part of the delay before the next wave is skipped. If enemies survive, the next wave eventually appears anyway after a timeout. The order of these waves is fixed rather than random, so destroying enemies quickly changes their timing but not which enemies are scheduled to appear.

Players can manipulate the dynamic enemy spawning to suit their goals. Survival players may choose not to destroy certain enemies or enemy waves in order to prevent more difficult enemy combinations from appearing (particularly in Stages 4 and 7), whereas score players may choose to speed kill successive waves in order to optimize the enemies destroyed bonus.

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Special Medals

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Stage 1

Shortly after the beginning of the stage, do not destroy the container on the third moving platform. If you leave it intact, the platform will disappear into a tunnel and reappear with a special medal in place of the container. The medal will stop flickering when it has reached the bottom of the screen. Collect it at this time to be awarded the max value of 100,000 points.

Stage 8

If you wait to take out the planet-destroying missile until after the timer has reached zero (you will have had to weaken the missile enough prior to this for it to work), the missile's weak point will reveal a special medal worth 30,000 points. Here the special medal does not remain onscreen long enough to collect it at max value.

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Stage 4 Secret Bonus

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Destroying the silos in the opening section of the stage will cause many medals to spill out. Destroying all of the silos will yield a secret bonus of 40,000 points.

In the second half of the stage, multiple formations of orbs will enter the screen. A special bonus of 10,000 points is awarded for each completely destroyed formation.

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Stage 5 Medal Carriers

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In this stage medal carriers do not appear regularly. Instead there are four locations where four ground medals are arranged in a diamond pattern. Hovering the player ship in the center of this pattern for about one second will make a medal carrier appear. Note that it is permissible to collect the medals surrounding the hover spot.

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Story

The year is 2050 (Cosmic Era), long after humanity embarked on a massive space colonization project in search of a "second Earth." Having settled across various star systems, humanity developed unique cultures and scientific advancements, yet simultaneously fell into conflict, sparking a succession of large-scale interstellar wars. The flames of war eventually reached Earth itself; a rebel force from another star system—possessing technology far superior to Earth's—brought a massive fleet led by a space aircraft carrier into Earth's orbit and demanded unconditional surrender. In response, the Earth Defense Force launched a top-secret operation codenamed "Viper Phase 1," the plan for which was to infiltrate the enemy carrier, gather data, seize a new type of enemy fighter, and then use that fighter to destroy the carrier.

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Development History

Viper Phase 1 was programmed almost single-handedly by Yoritaka Kasai, who handled the game's entire codebase — including system architecture, enemy behaviors, and boss encounters — while heavily struggling against the hardware limitations of the arcade board. To ensure broad appeal, simple controls and straightforward mechanics were maintained, though Kasai later made a business trip overseas to adjust the game's balance specifically for Western audiences, eventually introducing a medal-collecting mechanic in the New Version to cater to American player preferences.

Despite the tight schedule preventing full optimization during development, the foundational programming and system lessons from Viper Phase 1 directly paved the way for Seibu Kaihatsu's Raiden Fighters series.

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Version Differences

Viper Phase 1 exists in an original Old Version and a revised New Version. The American release, titled Viper Phase 1 U.S.A., is based on the New Version but also has some region-dependent differences.

Japan Old Version vs. Japan New Version

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Feature	Old Version	New Version
Secondary weapons	Limited ammunition (indicated by a gauge in the HUD)	Unlimited ammunition
Secondary weapon power	Fixed	Four power levels
Secondary weapon damage	Higher	Reduced
Power-up items	Power up the main shot	Also power up sub-weapons
Bomb detonation delay	Slower	Faster
Medal system	Simple	Expanded timing-based scoring
Medal carriers	Less frequent	More frequent

Furthermore, the placement of certain enemies differs between the two versions.

Japan New Version vs. USA New Version

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Viper Phase USA uses essentially the same revised gameplay as the Japanese New Version. By default it is configured with a second loop after clearing the game.

The only confirmed regional gameplay adjustment is the enemy bullet-speed rank curve. The USA version is slightly more lenient at low rank.

Other Versions

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Other region versions (Korea, Taiwan, Europe, etc.) are identical in content to the Japan New Version and only feature different license/distribution notices.

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Trivia

• The player 1 ship Judge Spear and player 2 ship Blue Javelin are selectable crafts in the Raiden Fighters series of games.
• In the Sony PlayStation release of Raiden DX, players can unlock the option to swap the standard soundtrack with music from Viper Phase 1.

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Gallery

See (Template Page)/Gallery for our collection of images and scans for the game.

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Soundtrack Releases

• Viper Phase 1 Original Soundtrack, a 2 CD set also featuring a superplay DVD was released by Ooparts in 2005
• Viper Phase 1.LP was released on vinyl by bootleg! Records in 2017

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References & Contributors

1. Shmuplations | https://shmuplations.com/viperphase1/
2. A.Y. Dayo | https://www2c.biglobe.ne.jp/~abfuku/raiden/rf_index.html
3. Primary info provided by CIT Seven Force
4. AI was used to analyze the game code and determine score calculations and enemy spawn routines

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