While paying her respects at her late teacher's grave, Asahi Sena witnessed a man tumbling down the stairs. Quick to act, Sena managed to catch and save him. It was then that she learned his name - Itsuki Tobari - and that he was in fact the younger brother of her former teacher. As they reminisced about the past, Tobari revealed that his sister had been killed by an 11-year-old boy who happened to be Sena's childhood friend. Now curious about what became of the boy who killed her beloved teacher, Sena and Tobari embarked on a journey to uncover the truth behind that fateful day.
