Friends Mamoru and Yuji are aimless young men stuck in dead-end jobs in a dreary factory in Tokyo. Mamoru, the more antisocial of the two, is obsessed with his pet project of acclimating a poisonous jellyfish to fresh water by gradually changing the water in its tank. One night, he inexplicably murders his boss' family and is sentenced to death. Yuji, left to continue the jellyfish experiment, befriends Mamoru's estranged father, and the two form a bond. But Yuji's attachment to the jellyfish is even stronger, and problems arise when he accidentally releases the poisonous creature into the canals of Tokyo.