When she was 18, Maki became pregnant and gave birth to her son, Tatsuki. His father disappeared, leaving Maki to raise Tatsuki alone and support him through university. Due to their close age difference, they resembled siblings more than mother and son, often going shopping and traveling together, sharing a close bond. During one winter break, Tatsuki invited Maki to a hot spring trip. Excited for what she thought would be another ordinary getaway, Maki had no idea of Tatsuki's true intentions—to confess something he had kept hidden since coming of age.