A year ago, Shio and her son Shirō became connected in Nishinikko. In fact, Shio had another twin brother named Masaki. Masaki was raised by a senior couple since birth and got along well with Shirō, but he did not know they were brothers. One day, Masaki was told by his foster parents that Shio was his real mother. Learning that the aunt he loved so much was actually his biological mother, Masaki became flustered. To tell him the truth and gain his acceptance, Shio decided to go on a hot spring trip with Masaki.
