Like in many other Japanese adventures, multiple endings also depend on the protagonist's behavior towards the girls who are trapped with him. Some puzzles have multiple solutions, and sometimes the solutions the player chooses lead to different endings. Most puzzles involves finding and manipulating inventory items. In many places there are traps that should be avoided, and puzzles to solve. The player navigates the protagonist around the facility over an isometric map, entering rooms and exploring them. Like its predecessor, the game is a hybrid of Japanese and Western adventure styles. Was this a murder committed by a human being, or some sort of an unknown evil force? The hero does not have much time to think, since whatever took the lives of the scientists also threatens to murder them. Exploring the abandoned building, the hero discovers the research staff died under mysterious circumstances.

The protagonist of the game, a high-school student, finds himself and other characters (mostly female high-school students) trapped in a marine research facility. Sosei is a follow-up to Dōkoku Soshite., featuring a similar story premise and gameplay.

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