30-year-old bachelor businessman Daikichi Kawachi encounters Rin, a girl he's never seen before, at his grandfather's funeral. Surprisingly, the 6-year-old girl turns out to be his grandfather's love child. Daikichi doesn't like children, but the cold attitude of his relatives towards Rin makes him uncomfortable. And then, the relatives' meeting to decide who will have custody of Rin begins at last...

What kind of clothes to buy her? What to feed her? What to do about nursery school? Daikichi's new life raising a 6-year-old girl is an uninterrupted stream of bewilderment. Rin looks anxious on her first day of nursery school, so Daikichi does a "pinky swear" with her, promising to pick her up as soon as he can. And Daikichi, who has no confidence he can live with Rin for long, starts thinking about meeting Rin's mother...

Daikichi finally meets Rin's mother, Masako, and he's shocked by her frankness. When they part, Masako asks Daikichi for a favor, and it's an issue that Daikichi can't avoid, as long as he's going to raise Rin. Daikichi tries to resolve it by having a heart-to-heart conversation with Rin, but he gets an unexpected answer...

At school, Rin is concerned that the disobedient Kouki is getting off track and getting a bad reputation. Meanwhile, when a typhoon hits, Kouki and his mom take shelter with Daikichi and Rin at their house.

It's the first anniversary of Grandpa's death, which means Rin and Daikichi have been living together for about a year now. Daikichi mulls over what he's lost and what he's gained since Rin came into his life...