Ouma's Smell
This was originally an analysis I wrote on Discord, transferred to be archived on this site.
I think he smells like clean laundry, slight hair gel and some generic cologne.
He doesn't iron his clothes (obviously, they're super wrinkly.) so they don't have that heated up clothing smell, it's just clean. (He may not seem so but he's high maintenance.)
He has good hygiene, and even uses a bit of cologne but he has horrible taste (/hj) and uses strong or "bad" smells that you can detect from a mile away. It's quite unique to him though, and once you smell the cologne you know it's him and he's lurking around the corner.
And of course, no one's hair is that neat without the help of some gel, even a little bit. Not a single strand is out of place, but his hair is still somehow outrageous. It's a contained chaos that very much works in his favor.
He's also known to have good fashion sense (mainly evident from his underwear description...) and most likely pick out scents and products that are a bit more on the expensive or "fancy" side to match his fashion and style. But just because they're fancy doesn't mean they always smell good; not to mention everyone has different tastes so what he picks out ends up smelling too strong for everyone else.
Either that or he plays into the childish side of his character and picks out stuff that a kid would wear or even a cartoonishly evil villain. He has a good cologne but also probably has that one fucking Smurfs perfume with the Smurf head on the lid.
Kokichi's the typa guy to have large lavish banquets only containing dishes like mac and cheese and chicken tenders. It's like giving a child a million dollars.