Keita Ibuki is a computer programmer who, with two of his friends, is developing and trying to sell a video game program. He has a chance meeting with a high Mototsumitama named Kuro. He gives her his dinner, a bowl of ramen, and tries to protect her when she is surprise attacked by another Mototsumitama. He loses his left arm, but she exchanges it with her left arm (Mototsumitama have enhanced healing ability). This creates a bond between them which makes her more powerful provided that he stays near her and supports her. Soon they, and Akane Sano, are targeted by the strongest Mototsumitama clan of the East, the Shishigami (Lion God) Clan in attempt to kidnap Sano and bring about the destruction of the coexistence balance, which Mototsumitama are supposed to protect.