Tsuma, Shougakusei ni Naru.

Keisuke fell in love with Takae when they met through work. They got married and had a daughter, Mai, before Takae was tragically killed in an accident. Ten years later, an elementary school student appears on Keisuke's doorstep saying, "I am your wife!"

Keisuke and Mai are thrilled that Takae has returned to them, even if it is in the body of a grade schooler. They devote themselves to making up for lost time together. Meanwhile, Takae is dealing with family issues in her other life as a fourth grader.

Mai starts working at a new job but gets depressed after struggling to connect with her first client. To cheer her up, Takae invites her to see a fireworks show. Keisuke decides to stop by as well and happens to bump into his coworker Moriya on the way.

Mai is on her second date with Renji Aikawa, who then asks her to show him around Tokyo. Additionally, Chika, the mother of Marika (also known as Takae), has been seeing a man more frequently. Marika is now also supposed to get to know him.

Takae is nervous to tell Keisuke and Mai about Chika's plans to move and remarry, but the two take the news fairly well since the family will still be able to meet. Takae tries to stay positive about the move and hopes it will bring her mother happiness.

After seeing Marika (Takae) with Keisuke and Mai, Chika presses her daughter for an explanation. Takae's reluctance to respond sends Chika into a rage. Keisuke witnesses the outburst and starts trying to think of a way to help Takae leave her toxic home.

Mai and Keisuke receive a surprise visit from Renji. Keisuke is shocked to learn that Mai has a boyfriend and depressed to realize that she might eventually move out. Moriya notices Keisuke's mood at work and tries to think of a way to help cheer him up.

Chika and the Niijimas work together to support Marika after her memory loss. Mai tutors Marika to help her with school while Chika continues to work toward becoming a better mother. Meanwhile, Keisuke is worried that he may have lost his wife yet again.