A year ago, Nanao married Shiro in Nishi-Nikko. In fact, Nanao had another twin brother, Masaaki. Masaaki was raised by an older couple from birth, and was close to Shiro, but did not know that they were brothers. One day, Masaaki was told by his adoptive parents that Nanao was his real mother. Masaaki was shocked to find out that his beloved aunt Nanao was his real mother. In order to tell her the truth and get her to accept it, Nanao decided to go on a trip to a hot spring with Masaaki.