The objective is to have multiple characters of various positions all survive in a flooded and destroyed metropolis. The player´s actions are fed back into the game and recorded. The ways in which a player deals with the other main characters will gradually change the shape of developing events.

Story
The place is Tomisaka City in Z prefecture. It is a typical city that has suddenly become the focus of attention after being chosen as the location for construction of Geo Frontier, one of the underground cities in the National Metropolitan Area Functional Decentralization Plan.

The Geo Frontier Project involved digging a giant hole in the earth and enlarging the surface area to create huge space. This new urban construction project was intended to make more effective use of the city´s limited land. With this project, Tomisaka City was on the verge of experiencing rapid expansion and development as it transformed into a giant underground metropolis.

Then one day in December 2010...
Against a backdrop of torrential record rain fall over the preceding several days; a party is underway in the underground city to celebrate the completion of Geo Frontier.

As the party is reaching its climax, the banks of the Haneshiro River that flows through the center of Tomisaka City give way, resulting in a flash flood that starts inundating the entire city area. With the ground softened under the record heavy rains, ground cave-ins and waterfalls form a great muddy flow that assaults the city. This flow engulfs large numbers of people and buildings, paralyzing the underground metropolis.

Among the people caught up in this disaster are a university student who had taken a job as a waiter at the party, a female university student who was a suspect in her older brother´s murder, and many other people of different ages and positions. They are all in for the fights of their lives as they strive desperately to escape.

Game Play
1. Multiple first-person roles
The player can become several different main characters - when one character´s scenario concludes, the player can switch to the next character.
The player runs through the same disaster timeline, but from different perspectives. This means that actions taken by a main character can affect the development of the game events for other main characters. These characters may come to each other´s rescue, or one of them may, in order to survive, perform an action that turns out harm one or more of the others.

2. Maintaining physical health - a matter of life or death
To survive in a metropolis that´s been devastated by disaster, it is essential to maintain physical health. Not only do characters lose the ability to perform as needed when their health deteriorates, but they may, at worst, fail to make it through alive.
Keeping a character´s health from deteriorating requires making the utmost effort to keep from getting wet. When characters get wet, it is crucial that they find a way to warm themselves as quickly as possible to restore body heat.

3. Struggle to survive the flood
The torrent of flood water that comes pouring in from every direction does more than just interfere with the player´s actions; it also brings the danger of being washed away and the possibility of dying.
There are times when prompt and decisive action is required, such as when assaulted by flash flood waters or when trying to escape powerful currents.