When his father remarried, Hajime was bewildered by the sudden cohabitation, but he found himself inexplicably drawn to his new stepmother, Tina. To shake off these feelings, he enrolled in a boarding school. Then, on the way home from his graduation ceremony, marking the end of his enjoyable student life... Tina came running toward him with a smile. Hajime's heart leaped at the reunion with his secret crush. That night, after seeing Tina off, she gave him a kiss, saying, "A present from me to Hajime-kun, who has become an adult..." Guided by his stepmother, the boy climbed another step on the stairs to adulthood.