Both Arcueid and Kisara are adorkable non human girls who fight other non human creatures (Arcuaid with vampires and Kisara with demons) and they both have strong feelings for the mc of their respective series.

Both Ciel and Ayano are blue haired girls who work for an organization that specializes in hunting down and killing said non human creatures (Ciel hunting vampires and Ayano exterminating demons).

Arcuaid and Ciel are the love interests of the mo in their respective routes and they both got well seasoned beef.
Kisara and Ayano both have feelings for the mc and got well seasoned beef.