A few I managed to think of off the top of my head:
Junko acting as a mom to Clownpiece
Koakuma using guns to fight/having a more serious attitude
Marisa and all the various fan interpretations of her (nonstop kleptomaniac, playboy, opposite of a playboy, stoic, shonen protag, jealous of Reimu, etc.)
Evil galactic empire style Lunarians
Flandre and Koishi hanging out together sometimes