I'm kinda surprised that there aren't more Eirin x Keine pics, given that Mokou x Kaguya is so popular and that normally leads to the whole "Pair the Spares" scenario.
Unya has gotten me to like this ship quite a lot though; Eirin has that whole "mature woman" vibe to her while Keine, who's usually portrayed as the more responsible and mature one to Mokou shows a more blushey side towards Eirin, which makes a nice dynamic to their relationship. Does that make sense?