(from ebookjapan):

New York City's underground aqueducts are rumored to be inhabited by strange creatures. In the darkness, like a huge labyrinth, there he is! A black grasshopper man saves a TV crew from being attacked by a monster man who turns into an alligator! The name of the man who appeared before the astonished crew was Kotaro Minami.

He had lost all memory except for being Japanese, his name, and the fact that he had escaped from somewhere. In order to solve the mystery of the mutant creature and to find out the truth about his past, Minami heads out to the world...! His next stop is Paris, the Opera!