Ima, Ai ni Yukimasu

Takumi's wife dies at the age of 25, leaving behind their son, Yuji, and a very special picture book. It tells a story of those who die- but are remembered by the loved ones left behind- going to a planet called Archive, and returning to visit when the rainy season comes. Suddenly, the picture book seems to come true, when Mio shows up... without a memory.

(Source: Anime News Network)