Rui raised Sei as a single mother. The father already had a legal wife, and Rui raised Sei alone with her own hands, even sending him to graduate school. One day, after the child-rearing was somewhat settled, Rui received contact from Sei's father for the first time in over a decade. His legal wife had passed away several years prior, and he hadn't been blessed with an heir, so he proposed that Rui become his second wife. A few days later, when Rui accepted Sei's invitation to go on a hot spring trip, she got into Sei's car despite her anxieties about the future.
