As sadomasochistic yakuza enforcer Kakihara searches for his missing boss he comes across Ichi, a repressed and psychotic killer who may be able to inflict levels of pain that Kakihara has only dreamed of achieving.

A large monster attacks Japan, but dies suddenly. While the people rejoice and bask in relief, the giant corpse left behind begins to slowly rot and bloat. If it explodes, the nation will be destroyed.