sero

considering one of his quirks, his canonically stated drawback is dry skin. his tape is made of skin cells ! the tape being produced is literally just his dead skill cells (to make this make sense let's pretend his skin replenishes fast than average ,, like a LOTTT faster) i'm typing this and my dog won't stop barking im gonna crash out and so sigh this sounds gross .. but the aspect that makes his tape sticky could hypothetically be his sweat (it'd have to have biological differences but quirks do atone for that kind of stuff so) & if we considered that the stick was his sweat then hypothetically he could train to increase / decrease the stickiness by learning to control how much sweat was released in the creation (allowing for him to create a kind of rope if there was no stick at all) (sweat theory also takes into account the way his work dehydrates him)

hagakure

so with the reveal of her literally being visible & her quirk just being light reflection hypothetically, if she learned to control that really well (to bend light), she could make light boxes where whoever she bent light around wouldn't be able to see (making their surroundings invisible) & further, if she could bend light, she could make lasers

todoroki

yeah the reason he can't control his fire as well as his ice is not soley bc he refused to use it but because it's a singular tempture quirk effecting the air around him (either freezing it or igniting it) & obviously fire just burns in oxygen & isn't containable which is why it always jsut does whatever the sigma it wants in the direction he's using it. & his ice is much more controlled because he can actually control what parts of the air he's freezing because it doesn't just burn

tokoyami + dark shadow

tokoyami quirk isn't sentiment they're conjoined twins & fumi has a quirk similar to whatever the fuck the name of that shadow jumping kid is but instead of going into shadows she rests in organs (but she can't rest in anyone else's because conjoined twin.. conjoined organs she'd die) & tokoyamis actual quirk (excluding the bird head..) is a real specific type of telepathy

aoyama

tldr: reverse photosynthesis he emits light right , & considering we don't know all the mechanics behind it & purposely ignoring its origin & the real reason for his tummy aches we can assume his stomach hurts because his body is eating at internal resources to produce said light (he's VERY dehydrated - which is a cause of tummy ache) because his body is using all the water in his body to produce the light (or like a shortage of electrolytes ) & his body isn't able to keep up with the water usage so he's constantly experiencing the side effects !!!!!!!1!1!1!1!1!

midoriya never quirkless theory

i think it would make sense if midoriya was never truly quirkless. following rlly basic theries of afo being his dad and the doctor stealing his quirk i think he had such a hard time and violent reactions bc he had a quirk factor but no quirk and his body was fighting the new quirk (s) bc it wasn't his og quirk but it was trying to take the spot if the og quirk,, and follow up here the reason he is the first one to devolp all the other users wuirks could be (if he had a dormant quirk, never taken just unknown like first) that his og quirk could've been some genre of a quirk enhancer mixed w afo & inkos quirk a quirk that pulled quirks to him (pulling all the mathers quirk to him & also potentially enhancing his ability for quirk analysis because his quirk was pulling on them & subconsciously feeding him information on how quirks worked

overhaul

this one might be like way canonically off, but also less of a quirk theory and more of a ?? he's goofy. his quirk literally just he can reassemble / disassemble everything like he can control atoms i think (matter blah blah) & he can obviously alter people's chemical makeup (or take parts out at least?) so literally.. he could've just removed people's quirk factors entirely whenever he dissembled them – he didn't need to experiment with eri to eradicate quirks (obviously, he couldn't have made the bullers without her dna BUT he didn't need her to remove quirks)

quirk #1

QUIRK NAME : undecided (oxidation)
QUIRK TYPE : EMITTER (?)
BASIC QUIRK INFO : The user can accelerate the oxidation process in the compounds making up materials. Their emotions highly impact the user’s quirk — residual from their father’s empathic-based quirk. Quirk can only be used when applicable — if an object requires moisture to use, the user can only use their quirk on it if there is enough moisture in the air to accelerate the process. Quirk does not work on items made of compounds that do not oxidize (ie; plastics, ceramics, etc).

quirk #2

the user can accelerate & control bone growth and manipulate the shape of their skeletal structure, either reinforcing it for defense or forcing bone outward for offense.

quirk #3

the user can ignite their own blood. death !!!!!!