Tsuma, Shougakusei ni Naru.

Niijima Keisuke is a man who remains broken hearted 10 years after his wife Takae passed away. But one day, an elementary school girl comes to his house and says that she is Takae, reincarnated as a different girl. Now Keisuke is trying to make up for lost time, while Takae struggles as a grade schooler with the mind of a woman in her 40s, trying create situations where she can meet Keisuke.