Trying to find a one-shot (I'm pretty sure it was only a one-shot).

Main character is a girl who watched the stars with her grandfather (who passed away) and stays in a house alone in the summer and meets a boy her age. At the end it's revealed that the boy is her grandfather sent from heaven to cheer her up and she goes to patch up her relationship with her grandmother(strained relationship).

I've looked though Angel/s, Astronomy, Star Admirer/s, and Ghost/s but still no luck.

Is it "Natsu wa Ginga no Ame ga Furu" from Sensei, Kiite yo?

Yes! Thank You! It bugged me for 2 years now.