Don't think so?
At least i can't recall any like that, there is always something even if it's romantic shenanigans revolving around quirky and influential people, there is nothing about an Isekai that leads to something like K-On, or, if there is, i have not read that manga.
...Oh yeah, can anyone tell me the name of one Isekai manga that i somehow forgot and it's driving me nuts?
It's one of those Otome Isekai stories where a girl reincarnates as a villainess and ends up being replaced by the heroine despite not being a bad person, so she decides to take advantage of the fantasy like aspect of the world to go after the Demon King himself and try to seduce him, if she can't marry a Prince and get all the luxury, why not go after the King that will eventually appear and try to help him not be destroyed by the heroine?
Cue a confused villain and his demon henchmen(and his one human helper) as this noble girl tries to give him food with aphrodisiacs inside of it, tries to sneakily make him sign marriage documents and all that with the Demon King being unable to kill this really weird noble girl who is smarter and deadlier than she looks despite acting like a crazy gold digger basically.
So yeah, typical Otome Isekai, only instead of the villainess being happy about losing her position, being worried about a bad end, or being so nice everyone loves her already, she is an unpopular girl that with her game knowledge decides to stop being a minor villain and go seduce the final boss of the game.