ironically, this is a shower thought.
i've often wondered what the hell is going on with shinsou's hair. why does it stick up the way it does. does he do it on purpose? it's obviously capable of laying flat on his head, we see it in the timeskip. of course, i have answered this question for myself and i've obviously made it monoshin.
shinsou's hair defies gravity in that way because he just doesn't take care of it. it's neglected, it's kinda gross. (quick sidenote, i dont know how hair works i have pinstraight hair). anyway, monoma fixes it. how?
monoma stays over at shinsou's one night, and when he's in the bathroom he looks at the products in there. AND HE IS ABHORRED. BECAUSE WHAT IN THE WORLD IS THAT BOTTLE? he immediately calls shinsou into the bathroom and points at it (he daren't touch it, its obviously tainted).
"HITOSHI. PLEASE DON'T TELL ME YOU WASH YOURSELF WITH 12 IN 1 SHAMPOO CONDITIONER SHOWER GEL BODY WASH MOUTHWASH TOOTHPASTE EYEDROPS DEODORANT PAINT THINNER PEANUT BUTTER MOTOR OIL."
the next time they're out, monoma walks him around the supermarket saying he needs to get different bottles for his shampoo and conditioner. he needs to wash his body with a different bottle too! no more 2, 3, 4 in 1! monoma will NOT cuddle him if he continues to use that GARBAGE.
he gets shinsou actual haircare products, for his hair type. and gradually overtime, shinsou's hair stops sticking up in the air like it's using uraraka's zero gravity. monoma likes to brush and wash it for him :)