Kouta was born when Yoko was 18. The father disappeared upon learning of the pregnancy, and Yoko, despite opposition from those around her, gave birth alone and raised Kouta by herself. Because they were close in age, their relationship was more like friends than mother and son. One day, Kouta invited Yoko on a hot spring trip. Kouta had something he wanted to tell Yoko once he became an adult, so he invited her on the trip.
