From MangaHelpers:

Shou lives out in the country. He has a big crush on his childhood friend Sora, but is afraid that she thinks of him only as a little brother. One day, Sora announces that she was abducted by aliens. Later that day, Shou confesses his feelings for her and she dies shortly afterward. Shou is still in shock from her loss, when an alien girl named Lila comes down from the sky. She has a disk that contains a brain scan of Sora, and she can run Sora's personality in her own body. She also wants to have a child with him. Will Shou be able to cope with all of these sudden changes, and will he be able to keep Sora with him after all?