Ren, the younger sister, has come home from studying abroad on a long holiday. Originally, there was only one room for children at home, so the brother and sister lived together in the same room, but with Ren's return, they start living together in the same room for the first time in a long time. Ren has an open, cheerful and proactive personality, and the brother is constantly shaken by his sister's unrestrained behavior while living in the same room. Before long, he begins to become aware of his sister.