父が再婚して、急な同居に戸惑いながらも再婚相手・ティナに何となく惹かれ始めていたハジメはその想いを振り切ろうと寮制の学校へ進学するのだった。そして楽しい学生生活も終わりを告げた卒業式の帰り道…。笑顔でこちらに駆け寄ってくるのはティナであった。密かな想い人との再会に心を躍らせるハジメ。そしてティナを送った夜「大人になったハジメ君に私からのプレゼント」と口づけを…。少年は義母に導かれ、大人の階段をまた一つ上るのであった―。

Hajime, bewildered by the sudden cohabitation after his father remarried, found himself increasingly drawn to his stepmother, Tina. Determined to shake off these feelings, he enrolled in a boarding school. On his way home from graduation, his enjoyable student life came to an end, he was greeted by Tina, who came running towards him with a smile. Hajime's heart leaped with joy at the reunion with his secret love. That night, after seeing Tina off, she gave him a kiss, saying, "This is a present from me to you, now that you've grown up." Guided by his stepmother, the boy took another step towards adulthood.