 If you liked
Sousou no Frieren
|
 ...then you might like
"Dam" in the Forest
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Both have a long-living mc who is trying to connect with humans and cherish the short time that they have with them.
If you enjoyed Frieren and Himmel, you may find something in Dam and Mishi. Dam of the Forest has no romance but it has a lot of meaningful relationships nonetheless.
Dam of the forest is set in a more modern world, so no monsters or mages or anything, BUT it does have a lot of deep character writing and has realistic (and tragic ;-;) development.