On a snowy Christmas night, college student Ryuusei witnesses a woman in cosplay being harassed by a man. He steps in to protect her but is stabbed and left dying. The woman reveals herself to be a clumsy demon named Yotsuba, and to save him she shares half of her life force with him, binding their existences. From that moment, they cannot be separated by more than a short distance without both perishing, and they have only one year to find the human who originally summoned Yotsuba—if they fail, Ryuusei will die and Yotsuba will vanish.

Ryuusei is a young man with a deeply scarred past, raised in an abusive household and struggling with his own inner darkness. Yotsuba, despite her cheerful and bumbling demeanor, carries the heavy weight of having once been a human who suffered so intensely that she became a demon. As they search for the summoner, they encounter people consumed by powerful negative emotions—rage, grief, jealousy—whose twisted wishes attract other demons. Ryuusei gradually awakens a latent ability to see the painful past of those he touches, a power that forces him to confront both the suffering of others and his own suppressed trauma.

Along their journey, Ryuusei and Yotsuba grow closer, their reluctant partnership deepening into genuine love. They learn that demons are born from human despair and that Yotsuba’s own origin is tied to a tragedy involving her brother. The search leads them to confront the lord of hell and the truth behind the summoner, a figure who set in motion a chain of sorrow. Ryuusei resolves to break the cycle by finding a way to turn demons back into humans and abolish hell itself, even if it means losing Yotsuba forever. The story explores whether love and acceptance can heal the deepest wounds, and whether two people bound by death can carve out a future where neither has to be alone.