The game follows Takeshi Kuranari and an amnesiac boy referred to only as "the Kid," who become trapped inside an underwater theme park along with a group of other people after a leak floods parts of the facility. Cut off from the surface and unable to make contact, they face a grim estimate: under the immense water pressure, the park is expected to implode within 119 hours. Gameplay has the player read through the story, making choices at key moments that steer its direction toward one of several possible endings.