A year ago Takumi's young wife Mio died from an illness, leaving behind him, their six-year-old son Yuji, and a homemade picture book, which described her going to a planet called Archive (where people who have passed away live as long as they're remembered) but returning at the beginning of the next rainy season. To Takumi's astonishment, exactly that does happen, although the woman who seems to be Mio has lost her memory. The book also says that Mio can only stay for the duration of the rainy season, and since her death Takumi has harbored doubts about whether or not she was actually happy with him, so he is reluctant to get close to her at first. As he helps fill in the gaps for Mio, though, they find each other falling in love all over again. But the mystery remains as to how she actually came to be there, and as Takumi eventually discovers, it is rooted in both their past and future.

(Source: ANN)