Him having erectile dysfunction and like no libido or being repulsed by the very idea of sex (or being asexual which is dumb since it don't mean he don't get horny. I think he is but also wants to fuck Takumi Get On My Level) is like the most straightforward thing but I personally like the idea the teenage boyisms and his high amounts of testosterone gives him Boners and wanna jack off and once he figures out how to project his sexual urges onto things that don't revolve around or involve human it stops being repulsive to him and leads to him having fucking weirdo fetishes (Although I still think he finds it annoying b/c when he gets hard even dumping ice cold water barely makes it go down and he got no choice but to Take Care of It lol)

I imagine when he was younger he'd get rlly attached to stuffed animals and talked to them and treated them like they were alive b/c it was the only way he could experience the barest facsimile of social interaction and does this even when he's far too old for it to be considered normal so he starts kissing them on the mouth w/ tongue and grinding on them and tearing holes in them to fuck. And watching a wildlife documentary and seeing the lions mating gives him a boner b/c he's still watching sex going on but not the kind involving any gross humans. I think he becomes Fascinated by piss and shit too b/c it involves His Private Parts and when he's surrounded by repulsive monsters all the time pee and poop is a lot less gross in comparison and it came outta his own body anyways. The gore is due to his desire to commit extreme acts of violence but he don't usually got any ways to express it so it ends up being redirected towards the pleasure of sexual release instead. Cutting himself makes him horny b/c it's one of the few sensations that are kinda sorta similar to having someone else touch him and his masochisms partially stem from this (he's got no control over the feeling of pain and when he's older the only way he can imagine physical intimacy is through acts of violence) He's jerking off pouring hand sanitizer on his dick

ANYWAYS I think Takumi's like kinda more horny than the average teenage boy b/c either he's got nothing better to do or to help him release stress but he's not that much of a pervert Esp when compared to Eito. I think having Eito up there would rid him of the desire to think or do anything sexual there's few things he could find less appealing than having Eito watch him jerk off and provide a running commentary. He couldn't do it even if he wanted to. Unfortunately he's instead subjected to sharing Eito's many deranged sexual interests; Eito's fully aware his psychosexuality is Fucked so watching Takumi get turned on and be horrified by all the weird shit he wacks it to is rlly amusing to him