Resistant-to-magic! Yuu
I've been playing with the idea of making my Yuusona not only magicless, but also somewhat unsusceptible to spells from Twisted Wonderland because they're from a world where magic is absent. Yuu may not be able to perform spells, but on them magic (from potions and spells alike) has a weakened effect due to them not being native to Twisted Wonderland.
Ex¹: Grim flames do not burn Yuu alive, instead they just feel like touching something that's too hot.
Ex²: Jamil's signature spell gives Yuu a headache instead of hypnotising them.
Of course, the amount of effect that the spell loses depends on how strong of a mage the caster is, but as a general rule, Yuu cannot be lethally damaged by a spell and most students'magic is innocuous to them.
I didn't concoct this characteristic just to give our powerless prefect some leverage (though they certainly deserve it with how much bull**shit the characters give them), but also because to me it makes Yuu surviving an overblot more believable — they are resistant to magic, and while overblots are powerful enough to bruised them up, they cannot kill them.
I also think it'd be funny if Yuu could drink potions or magical poisons just because they're immune to the effects and they like taste. Everyone gets a good scare when they see them sip a notorious poisonous potion like it's a soda, before remembering that Yuu is resistant to them.
Tell me what you think :3
Also this isn't an original idea in the slightest, so feel free to use it for your ocs/yuusonas too!