The oneshot is about the Male mc going on a hiking trip in which (for reasons I dont remember) starts talking to his dead childhood friend who is in heaven. Where they have their emotional back and forth. She explains that when your remembered in heaven you get paid everytime your remembered. He gets over whatever trauma/emotional thing. Then he had discovers a comet (?) I believe and names it after her for a decently satisfying end. Sorry for being vague but this just popped into my head today and it was only saved on my kissmanga list (which is now very dead) so I ask for your help orz.
Oof I remember reading this oneshot. I believe the male mc's childhood friend was his girlfriend. I believe the girlfriend got into a car accident. The person who caused the crash also died. Even after her death, the male mc kept talking to everyone about her. Thus, she became really rich in heaven. I think the girlfriend even helped the person who caused the crash because he was really poor. I would search for it on mangadex but mangadex is down
I think what you are looking for is Magi no Okurimono. Although it is a single volume manga rather than a single chapter.