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'd suggest checking out the manga from the point where the anime ended. Sometimes, the anime might make some minor changes, but the general plot continuation should be clear. You could also look for recommendations from fellow fans to get a precise starting point.