What's wrong with me, falling in love with my childhood friend's father? Nao is a girl who lives in a small rural town in the mountains. As she approaches high school graduation, she peacefully spends her remaining days as a student taking care of her somewhat unreliable childhood friend, Hiroki, who has been with her since she was little. Hiroki's father, Masaki, watches over them kindly. He has been raising Hiroki single-handedly since his wife died of illness almost as soon as Hiroki was born. Wanting to help Masaki, Nao goes to Hiroki and Masaki's house every morning to help out and adores Masaki like her real father. On the day of Hiroki's high school graduation, he finally decided to confess his feelings to Nao, whom he's been in love with for many years. However, after graduation, another childhood friend, Sayuki, stopped Hiroki. Sayuki had decided to move to Tokyo alone to attend university, but she brought Hiroki to her home to listen to her worries. --At night, Hiroki was supposed to tell Nao how he felt, but what came out of his mouth was, ``I'm going to Tokyo with Sayuki.'' Sayuki begs Hiroki, and he chooses Sayuki over Nao. It happened. Later, as the two boarded the train to Tokyo, Nao saw them off cheerfully as usual, but on the way home she cried alone, confused by the fact that her love had broken up before she realized it. Hiroki's father, Masaki, found Nao hurting and offered her a helping hand. Several years have passed since then. Nao has grown up from a girl to an adult woman. Even after Hiroki disappeared, she spent time with Masaki, living like a newlywed couple. After four years, Nao at 21 has come to love Masaki, whom she admires like a father and loves him as a man. However, Masaki continues to think about his late wife. Nao spends her days worrying about a love that will never come true and continues to console herself. However, one day, the relationship between the two suddenly deteriorates. I know that you still love your wife.'' But.'' ``I want to be by your side.'' Masaki gently kisses Nao, whom he cherishes like a daughter, and extends his hand to her soft, unexplored body...