Yuki was born when Naoko was 20 years old. His father disappeared, and Naoko raised him alone, overcoming the objections of those around her. Sometimes kind, sometimes strict, she raised Yuki as a mother and father figure. Perhaps thanks to her efforts, Yuki was able to get a job and live in a dormitory. Some time passed, and Yuki had a long holiday and returned home to his hometown, so Naoko took him on a family trip to a hot spring.