Try the custom AI to help you find products that Reddit loves.
Amazon is price matching Emanon
You mean this?
omoide emanon is a good short story that I like a lot but it doesn't really fit what your friend seems to like, about a girl who has lived through the entire history of the universe and ends up meeting someone who she admits the whole story too, here
the gods lie is pretty good as well and fits pretty closely with some of the stories you listed, only $10 on amazon, here It's about a young student who meets a girl with a secret and becomes involved in her life, and kinda follows parts of the 4th storyline you mentioned
as mentioned by others solanin is pretty good but I don't think it really follows any of the stories you mentioned, maybe the 1st storyline a little?
don't get him a girl on the shore, imo it's pretty bad and generally reserved for those who specifically like the mangaka, Inio Asano. biggest reason why though is that if someone asks about his manga and then finds that, they'd be in for a surprise-lots of nsfw scenes between basically middle schoolers, would not be a good look.
also you should probably establish what kind of budget you're operating on