A promised past and returning where one belongs. The underwater theme park, LeMU. Takeshi Kuranari, one of the park guests, is suddenly involved in a freak accident. And he finds himself stuck in LeMU with a number of other survivors. Because of the system's failure, the water pressure will slowly crush the facility. The time limit till implosion is 170 hours and 17 minutes. Will they be able to escape to the surface!?