"Aim to be the kingdoms best Beast Tamer for the sake of a great ambition."

Crus is a man who lost his past memories after suffering a serious injury. Haunted by an inexpressible sense of anxiety, he wandered from place to place, working as a sort of bodyguard to escape it. One day, he met a "beastman," a Gray Cat tribe member named Chloe. She, too, was wandering, searching for the ones who massacred her tribe.

Chloe makes a proposal: "Become my Beast and aim to win the Grand Tournament held in the royal capital."

Her enemy might be there. And, she says, he might be able to recover his lost past. Crus accepts her proposal, and together with a twisted comrade in the form of a slave, he throws himself into the battles.