Tsukioka Natsu is 28 years old. He works for a printing company in Tokyo. One day, Tsukioka Natsu hears that Nagumo Mizuki died. They were in a romantic relationship when they attended the same university. They broke up after Nagumo Mizuki suddenly told him that she wanted to end their relationship, and she disappeared afterwards. He didn't hear anything about her for the past 7 years after their breakup. Tsukioka Natsu attends Nagumo Mizuki's funeral, where he meets a young child named Umi. He is surprised to learn that Umi is Mizuki Nagumo's daughter. Nagumo Mizuki's mother talks to him and tells him that Umi is his daughter.