Séraphin

Its -in ending obviously shows it's masculine. Why do people feel it's common but Séraphine and Seraphina are very upper class?

I would caution anyone who likes this name that it has a strongly negative connotation in Quebec, and quite possibly in Canada more generally. As another commenter has mentioned, it is the name of the villain in a famous French-Canadian story. A good comparison, I think, is the name Ebeneezer in English. They might call a miser "un Séraphin" the same way I might call someone "a Scrooge".

Cute but rare and old fashioned, but cute.