Chinatsu and his older brother, Fuyuki, have been trained by their father to become professional assassins for their whole lives. However, Fuyuki is slain as a result of Chinatsu failing at his first job. Chinatsu is discovered by a blind boy who lends him a shoulder to cry on.

The trauma still haunts Chinatsu five years later, and he is unable to kill any of his targets as a result. While waiting around the streets, he recovers a stolen object owned by Kasumi, the blind boy he had met back then. As a token of gratitude, Kasumi invites the assassin to his home that is located in a traditional Japanese inn. Chinatsu learns that the boy sees himself as a burden to his family due to his disability.

Despite being complete strangers, Kasumi feels a connection with Chinatsu and asks him to be his friend, to which the assassin readily agrees. But Chinatsu discovers more from being around Kasumi's kindhearted nature, and he realizes he may have found a way through the darkness of his life: a light worth protecting amidst the abyss.