You are killing me here. It is such a sweet death.
I realize that there's something about a concert or some such, but other people have covered that in more detail than I feel like. I have but one gimmick, and I am going to milk that gimmick for all it is worth.
Mind you, I'm well aware that given Tsumugi's inclinations, it would be highly disingenuous of me to ever consider her Mai Waifu material. At the most, I can only observe her from afar, which is probably why the thought "Mugi-chan in a maid outfit" quickly turned into "Mugi-chan in a maid", and all that entails.