In a post-apocalyptic world covered with water, Wadatsumi, a person who lives in what appears to be the last piece of land, finds a mysterious girl dragged by the waves of the sea. Where does she come from? Are there other lands in this world?

From Taruby:
After 'The Great Sinking,' civilization on Earth crumbled as the world was drowned in the ocean. One tiny band of survivors eke out a living atop the ruined remains of a skyscraper. Wadatsumi, a young tomboy, is saddled with the care of four elderly gentlemen, until a chance encounter with a group of pirates and a mysterious woman turn her world upside-down.

This is Daikichi Kamiyama. A College Student at Toudai University. He had came back to his home town to attend such a prestigious University. He happened upon a cafe where once stood a great wrestling arena lead by the "Amazoness kitty." Now three daughters remain running it. Yukihyou (Who has taken a sudden interest in him.) Ferris (A rather ditzy young woman.) And Leona (A Tsundere-ish big boobed girl with a rather "Unique" Ability in the wrestling ring.) Join Daikichi "sandbag" Kamiyama as he endures the trials ahead of him with these Bombshells.

The Tokyo area has been hit by a gigantic earthquake. In the midst of this chaos, Akito and Yumi meet and together they start traveling through the city in order to survive.