A flashback is shown with Yu, Yuko, and Kuze in their younger days as high school students. At this time, Yu and Yuko have not seen each other for ten years. In the present day, Mizuki is staying over at Renji's for the time being until she enters high school, and does not have much to do while Renji studies for exams. Renji's mother introduces Kuze to Mizuki, who discovers some of the things Renji was trying to warn her about him might be true. Mizuki and Kuze spend the rest of the day together, and the two become more familiar with each other.

In the past, Yu finally comes to terms with his love for Yuko, but must turn down Nagi first. After Kuze plays his violin for Yu and Yuko, Yuko starts crying because the music is so beautiful and runs out of the room; Yu chases after her to the school roof. There, Yu professes full devotion to Yuko, and she finally reveals to him what she has been hiding this whole time. Her older adoptive brother has been physically abusing Yuko for years, and she infers that this could have all been avoided had Yu merely said he wanted a younger sister back when they were at the orphanage together.

In the past, Yuko is back at school while Yu is still missing. Both of them realize their love for each other, and are helplessly in love. At home, Yuko's brother goes on a rampage and throws Yuko onto the wall, where Yu intervenes and is beaten by Yuko's brother. Yuko's brother takes a look at Yu's sketchbook and takes it with him into his room, where he goes insane and starts drawing his deceased sister. He burns the drawings along with himself. In the present, Mizuki receives charms from Chihiro and Kei, which are keys to the roofs of the two Otowa Academies. Kuze realizes that he wants to live and that now he is all alone.

In the past, Yuko and Yu are now living together again. Yu is getting drawing lessons from Nagi. Yuko meets an orphaned girl named Miki, who was intended to commit suicide with her parents. Soon, Yuko and Miki become friends. Miki meets the young Kuze, and Kuze gives her his green ribbon, which he uses to tie a side ponytail on her. Yu and Yuuko decide to meet after Yu's work on Christmas, but before Yu gets there, Yuko gets into a car accident. By the time Yu and Miki arrive, Yuko is already dead. Yu remembers that Yuko gave him the key to the school roof to keep for safe keeping, and how she said to give it to anyone who is sad or lonely.