I noticed there were a few images under fumika that could probably use a different tag given they're referring to different characters, and I even noticed Tenebrous already brought the point up in post #219177. The main Fumika's are pretty easy to tell apart, post #657580 for example. The girl on the left is known as Fumika フミカ in the credits and the right is known as Mikawa Fumika 美川文歌. Mikawa Fumika used to be one girl with two personalities named "Fumi" and "Mika", but the latter became a separate entity later on, the girl on the left. I don't think there are any young images of her on Danbooru, though (at least on my quick look through). I thought post #219177 (and I have confirmed it looking on gofu's site) was Fumika 文伽 from episode 10, who is a completely different character just with the same name reading. Rather than using "Fumi" or "Mika", I think they should just be tagged as they are in the credits:
Silver-haired girl: fumika
Black-haired girl: mikawa_fumika
Little girl: fumika_(shigofumi_ep10)
Fumika doesn't have a qualifier (none of the single-name characters in Shigofumi do currently), but I don't think she needs one as there are no other prominent single-named Fumika characters.