Hakoniwa no Soleil

After visiting her late teacher's grave, Asahi Sena encounters a man who falls down the stairs, which she helps save. The man, Itsuki Tobari, is revealed to be her teacher's younger brother. They discuss past events, including the death of Itsuki's sister and an 11-year-old boy, Sena's best friend, who was responsible for her death. They seek to uncover what truly happened on that tragic day and what has become of the boy who caused it.