Des：One year ago, Nanao tied the knot with her son Shiro in Nishi-Nikko. In fact, Nanao had another son named Masaaki, her twin brother. Masaaki was raised by a senior couple from the time he was born, and was close to Shiro, but he didnt know they were brothers. One day, Masaaki learns from her foster parents that Nanao is her real mother. Masaaki is upset when he learns that his girlfriends favorite aunt Nanao is her biological mother. In order to tell her the truth and have him accept her, Nanao decides to go on a hot spring trip with Masaaki.