I... don't really listen to character songs often, but if the solo Love Love songs count, I think some of them are really good!

Arifureta Kanashimi no Hate for Eli is my favorite of those, though!
Darling!for Maki
Nico puri♥Joshi dou for Nico might be the most character song-ish though! (This is the only video with the full song I could find... xD)