Hoshiai no Sora

Main character lost his family in a fire eight years ago. But he suddenly receives a letter from his allegedly alive sister. The return address is his hometown, so he goes there to confirm the truth. A mysterious girl at the station lends him a spare umbrella. The long search brings protagonist to an old mansion. To his surprise, the same mysterious girl comes out and call another girl with the same name as his sister had. Protagonist does not remember sister's face, so he stays at this mansion for a while to check things out.

[From vndbreview]