This adventurous story of a boy named Uri and an old man takes place in the cosmic Milky Way where the starfish live. This is the tale of their fantasy journey in search of the mysterious monster fish.

While walking through the streets of Tokyo, Linn Suzuki comes across a strange device sticking up from the sidewalk. Suddenly, she is set upon by thugs and is helped by a beautiful stranger who takes them all down. It seems young Linn has fled Deep Kyoto from her cruel mistress and has traveled to Edo where she hopes to find her long lost brother, who was last seen working for the Kuon Detective Agency. By chance, this stranger happens to be Miho Kuon and lets Linn stay with her (nicknaming her Kotetsu, or Little Tetsu after her brother, Tetsujin). However, a mysterious agency called the Syndicate are after Miho and Linn is now in the thick of things.

On what apparently is a parallel world, time flows in a much slower pace than normal. The ocean remains on a solid state of matter as the eccentric individuals who inhabit this land casually wander over it.