These two are written with very strong autistic coding, I'm curious if author is doing this consciously. From how they said they both don't like changes, Runa literally creating a script for the meeting, to Ruka's anxiety and limerence(obsessing and copying) towards Yamada. Even Runa's speech pattern(speaking about herself in third person) can be attributed to autism.
Anyway, these two are really cute and I hope we'll get more of them together.