"Beast men" and humans have always been locked in conflict. Although treaties exist in an attempt to halt their battles, the prejudice between them can never be eradicated. Yakuza Haruomi Tengeji is an outlier among his group, who quietly laments that he must fight against the beast men. However, his fellow group members know that he only feels this way because of a certain "pet" waiting for him at home. Ever since being taken in by Haruomi years ago, the half-wolf and half-human Rou has shared a special bond with the man. Rou's oath to follow Haruomi anywhere binds their paths tightly together, even as it leads them both to the depths of hell.