Personally I ship Mizuki with the highschool teacher.
...did they even interact once?
If we talk about the one with glasses then yes. When Kasumi and Sakurako went flower viewing in the school, nearly everyone come andwhen the students ask the teachers about having a sip of a beer,he said no and told to Mizuki it was the same for him and Mizuki to reply he have no interest.
Well, it's the only interaction i remember.