As a single mother, Yuriko Kasai raised her son Izumi Kasai alone. Izumi Kasai is now an adult and works for a record label, but Yuriko suffers from Alzheimer's disease. She is even losing memory of her own son. Izumi takes care of his mother and recalls long ago memories with his mother, but he faces a case that took place in the past. That case is something that is unforgettable to him.