A replica falls in love, and suddenly being a replacement stops feeling like a curse. She wears her hair up so one person knows it's her, not her original, and that small act becomes the entire reason she wants to exist. The show strips away everything but this: a girl made of borrowed pieces discovers the one thing that can't be copied is the choice to show up for someone tomorrow, and the day after that.

A girl who came into being when Sunao wished for a substitute takes her place whenever needed: on sick days, on test days, or when Sunao simply does not feel like going to school. Nobody knows she exists, and everything about her is borrowed. Then she befriends Sanada, a classmate who becomes the first to notice she is not the real Sunao. She asks him to talk to her only when her hair is worn half-up, so he knows it is her. They skip school together and promise to meet again tomorrow and every day after. As they grow closer, she realizes she has feelings for him, with no idea what falling in love means for a replica.