Marine Benefit plays like a fairly typical vertically-scrolling danmaku shooting game, in which the player's character is always facing towards the top of the screen, shooting at anything that moves, avoiding and weaving between enemy bullets, and confronting difficult bosses at the end of a stage.
There are 4 levels of difficulty: Easy, Normal, Hard, and Lunatic. Each difficulty level features differences in the number of bullets fired by each enemy, rate of fire, variations in the bullets' pattern of movement, and the number and type of enemy Spell Cards used.
The player will traverse 6 increasingly harrowing stages through the course of a regular game.
Once the game has been completed without continuing on Normal or higher difficulty, an Extra Stage is unlocked, available for any character that has accomplished that feat.
A character's "shot" is the player's primary method of attacking enemies. While the shot's attack area and behaviour varies depending on the character type the player has chosen, the shot can be powered up by filling up the Power Level by collecting power items.
Special Ability: long-lasting bombs, fast increase in oxygen meter
- Forward-Focus Type (前方集中装備)
- Shot: Infrared Detector (「インフラレッドディテクター」)
- Bomb: Red Sign "Outer Red Boundary" (赤符「赤外結界」)
- Homing Type (自動照準装備)
- Shot: Homing Laser Sight (「ホーミングレーザーサイト」)
- Bomb: Red Sign "Red Dream Enigma" (朱符「夢想妙朱」)
- Infinite Flowering Type (無限花序装備)
- Shot: Scarlet Flame (「スカーレットフレーム」)
- Bomb: Red Sign "Red Yin-yang Orbs" (緋符「陰陽緋玉」)
Special Ability: item collection area is wide, fast increase in hydrogen meter
- Trailing-Option type (追尾配置装備)
- Shot: Star Imprinting (「スターインプリンティング」)
- Bomb: Blue Sign "Sirius Movement" (青符「シリウスムーヴメンド」)
- Light Speed Piercing Type (光速貫通装備)
- Shot: Constellation Laser (「コンステレーションレーザー」)
- Bomb: Blue Sign "Blue Spark" (藍符「ブルースバーク」)
- Direction-switching Type (方向回転装備)
- Shot: Sky Illumination (「スカイイルミネーション」)
- Bomb: Blue Sign "Blue Sky Sunlight" (蒼符「ブルースカイサンライト」)
Special Ability: main shot is strong, gains back power easily
- Wide-Narrow Dual Type (広狭二種装備)
- Shot: Kanako's Divine Virtue (「神奈子様の神徳」)
- Bomb: Green Sign "Spring East Wind" (緑符「スプリングイーストウィンド」)
- Superwide Type (超広範囲装備)
- Shot: Suwako's Iron Rings (「諏訪子様の鉄の輪」)
- Bomb: Green Sign "Jade-colored Sea" (翠符「翡翠色の海」)
- Thermonuclear Explosion Type (熱核爆弾装備)
- Shot: Submarine Sun (「サブマリンサン」)
- Bomb: Green Sign "Green Flash" (碧符「グリーンフラッシュ」)
A character's "bomb" is the player's limited-use method of getting out of difficult situations. A bomb's attack area, duration, and power varies depending on the character type the player has chosen, but it typically deals heavy damage to every enemy it touches, in addition to cancelling out any bullets in the bomb's way. The player's character becomes invincible during and for a short time after the bomb's effect wears off. At the beginning of the game and any time your character respawns, you will start off with 2 bombs or whatever the number you had before (whichever is bigger).
Extra bombs are obtained through collecting Hydrogen items. The small H item increases (moves it down) the hydrogen meter by 1 point. The large H item increases the hydrogen meter by 12 points. The increase in H meter is twice as much for Marisa. When the meter reaches the lower blue mark (224/256/288/320 items) the player gains an extra bomb and the meter resets.
As of the 2013 version, the player is limited to 8 bombs; if a bomb is collected when the player already has the maximum it is simply lost.
With default settings, you will start off with 3 lives. You can lose a life by getting "hit" by an enemy attack.
The hit box for your character is quite small in comparison to your on-screen sprite, approximately only 5 pixels by 5 pixels in size. It is marked by the red dot.
If you have bombs in stock and the Bomb key is pressed within a short time of the player's character being hit, then the hit can be negated and countered with a bomb. This deathbomb time interval only lasts about 0.1 seconds, after which you will lose a life as normal.
The player is awarded extra lives by collecting Oxygen items and grazing. The large O item increases (moves it down) the oxygen meter by 2 points, and the small O item increases the oxygen meter by 1 point. The increase in oxygen meter is twice as much for Reimu. The oxygen meter can also be increased by grazing (see below). An extra life is awarded when the oxygen meter reaches a certain point (marked by the lower orange arrow, equal to 64 oxygen items) and the meter resets.
Upon losing all their lives, the player is given the choice to continue right where they left off. However, if you do continue, your current score will be reset. You may continue as many times as you like. If you choose to continue, you will start over from the beginning of the stage, but with 5 lives and 4 bombs, instead of the normal 3 lives and 2 bombs.
As of the 2013 version, the player is limited to 8 lives in stock (i.e. 9 lives total); if a life is collected when the player already has the maximum it is simply lost.