Yū lives alone at a boarding school, enjoying a fulfilling student life that has now come to an end. As he walks home after graduation, feeling a little lonely, his stepmother, Kyōko (also known as Ando), approaches him with a warm smile. They share their excitement about reuniting with each other, and later that night, they celebrate their graduation together... just the two of them. Their conversation fills the time they spent apart, and then Kyōko leans in softly, her lips touching his gently, whispering, "This is my gift to you, grown-up Yū..." This day marks another step forward in their journey towards adulthood.

寮制の学校で単身暮らしているゆう。充実した学生生活も終わりを告げ、とうとう卒業式。少し寂しい帰り道、笑顔で駆け寄ってきたのは、なんと義母・和咲であった。憧れの女性との再会に喜びながら、夜は2人きりで卒業祝いを…。離れ離れだった時間を埋めるように語り合う2人。そして「大人になったゆう君へ私からの贈り物―」と和咲のほのかに濡れた唇が彼の唇を静かに塞いで…。この日、大人の階段をまた一つ上るのであった―。