One idea could be a story where Mash teams up with an unlikely ally from a rival school. They start off not getting along but through various challenges, they learn to work together and combine their unique skills.
Another option could be a student from a different magic school who is jealous of Mash's popularity and unique abilities. This student could use dark magic to try and bring Mash down.
I'm not sure specifically as the term 'ln op magic novel' is rather unclear. It could potentially be about a novel that involves some kind of magic system that is very powerful (op, which might stand for overpowered) and perhaps has some elements related to natural logarithms (ln), though that's a very strange and unlikely combination in a normal novel context.
Since I don't know the specific 'Muscle Magic Novel', I can't say for sure who the main characters are. But they could be bodybuilders or athletes who discover the muscle magic.