Ok...?
I get that she exists as a vehicle for Natsuki and Junpei's relationship to create jealousy & help Junpei make up his mind that he maybe likes her (or doesn't and is still hung up on Miyako) but that was just insanely forced. Maybe it'll backtrack on all this in the next ch then it's ok-ish, since it'd be some sort of 'theyre 15, hormones flying all over, doing stupid things in the moment' but still really odd way to go about it.