I know it's not completely mischievious, but Natsuki and Shizuru don't seem like the type to go all Weasley Twins with the Marauder's Map. More like, I feel they would use it to creep on their classmates...Shizuru would probably be like, "Ara, is that Haruka's name? And Yukino's name? Miss Chrysant, I do believe that is calling the kettle black." And Natsuki would probably be like, "Oh, so that's where Nao goes when she ditches class...*evil grin*"
I was actually pretty pleased with how her expression turned out.
If I had the time and motivation (motivation I have, time i do not) then i would use my brain to come up with scenarios of the Mai group at Hogwarts (but not an x-over with the actual HP)
Miss Maria would be the McGonagall, no doubt about it.