Manji has an unfortunate reputation as the fearsome bodyguard Red Dog who indiscriminately kills people, including his own employers. Although all his actions belie good intentions, he is unable to find work in most towns. One day, idle and bored, he meets Karu—a strange boy who falls from the sky and lands on top of him.

Karu tells Manji to be wary of Toys, a type of doll that moves autonomously. When the two come under attack, Karu is surprised by both Manji's skill in cutting down Toys with a katana and his reckless disregard for his own life. Manji is seriously injured after the fight, but Karu exhibits an ability to transfer the wounds to himself—forming a pact between the two.

As Karu's pact holder, Manji receives a tentative welcome into the organization called Cards. Its ultimate goal is to find Alice, the Toy-making factory from which the insane inventor AAA unleashes his murderous creations upon the world. What shocking secrets will Manji uncover as he joins Cards in the battle against AAA?