Yukisada Tamura is an ordinary boy in his third year of junior high when he becomes fascinated by Komaki Matsuzawa, a mysterious classmate who claims she was born on another planet and is trying to return home. He confesses his feelings to her, but soon after, her grandmother dies and Komaki moves away. They keep in touch through letters for a while, but the correspondence stops around the time of high school entrance exams. Entering high school, Yukisada notices Hiroka Soma, a classmate who was severely bullied in junior high and now isolates herself. Unlike the other students, Yukisada reaches out to her, offering encouragement that slowly rebuilds her self-esteem. Hiroka falls in love with him and confesses. During this time, Yukisada’s best friend, Shinichi Takaura, has remained in contact with Komaki and mentioned Hiroka in their letters. Komaki eventually writes to Yukisada asking who Hiroka is, forcing him to choose between his old love and his new one. The story follows these intertwined relationships through the seasons, capturing the pain, heartbreak, and exploration of young love. A side story focuses on Shinichi Takaura and his younger half-sister Io Tamai, who despises any talk of romance; Shinichi attempts to rehabilitate her in matters of love.