I’m mixing legends and tropes and weird biology willy-nilly someone should probly take this idea away from me but i’m having too much fun
Japanese dragons are heavily associated with water and have a precedent for turning from dragon to human or vice-versa so dragons-disguised-as-humans makes perfect sense and also i can model izuku after a fish
specifically the electric eel, and i now know there’s an electric eel in tennessee that runs a twitter account and i think that’s beautiful
anyway both izuku and inko can generate electricity and have electroreceptors, which means they can sense the electrical fields of other living things a la sharks/platypus (i think, if i’m butchering science plz tell me). it’s stronger in the water, and they are great swimmers, but they can still sense living things in close proximity and have a shock strong enough to kill. they also tend to shock ppl who startle them or they don’t like. hmmmm bill always gets a static shock when he pokes izuku i wonder why hmmmmmmmmmm.
mitsuki and katsuki on the other hand are modeled a little more after snakes and can sense infrared. they also secrete pseudo-nitroglycerin like katsuki does in canon, except it’s in their mouths so they can literally spit explosions or leave nitro-drool on things, including themselves, to ignite later. cuz reptiles don’t sweat and all that good stuff.
dragons in general have the same taste/smell combination as snakes (jacobson’s organ) and exhibit a “flehmen response” (like a cat or horse wrinkling their upper lip) which mmmmmaybe does double-duty for infrared sensors? pit organs would probly work better on the surface of the skin rather than underneath the lip or whatever but ¯\_(ツ)_/¯
basically dragons “see” a lot more than you think and when kacchan sneers a lot of the time he’s actually using his freaky dragon senses