Stranger in the Twilight

One summer day, a boy named Tatsuomi Shiba arrives in the town where Riko, a second-year junior high school girl, lives. His family, who is related to the chairman of a big corporation, is welcomed by the neighborhood, but Tatsuomi keeps his distance from everyone around him. But Riko won't leave him alone, and they make happy memories of their summer together. On his birthday, Riko promises to give Tatsuomi a gift. However, their carefree days come to an end along with the end of summer. Who is the person that is her first love?

(Source: Kiss, translated)