I went and bought the Gekkan Shoujo Nozaki-kun fanbook, and as many of you might remember from many scanlated chapters ago, Tsubaki-sensei once mentioned that the protagonist was supposed to be Nozaki-imouto.
Incidentally, Mayu was originally supposed to be another Nozaki-imouto:Yeah, the photoshop and typesetting looks like crap, but that’s why I’m a web novel translator, and not a scanlator. Lay off me. xD
EDIT: Oops, forgot the text on the side.
“Mayu was originally a woman, but because she wouldn’t get along with the other guys (in particular, Mikoshiba), she became a man. A scene of high school boys nervously fidgeting before the silent middle school girl.
Incidentally, although the two brothers of the Nozaki household lack enthusiasm, the current little sister is always super energetic (like her father).”