Illustrious: (0.8 - 1 is recommended)
To get the twink look as in the original source, I suggest to use the tags "mature male" and "slender" where necessary for a less feminine, shota-like, and also not too bara'ish Usui. If you do use these tags, make sure to also include "facial hair" in the negative section too to avoid from generating an actual older guy.
School uniform:
white collared shirt, sleeves rolled up, red necktie, black belt, yellow pants, brown school shoes
optional: green blazer