I think the idea is that he's trying to be erotic because he knows Kazunori is a virgin and doesn't think he has a chance with him unless he can get him into bed because, as it shows, Kazunori isn't sexually aware of him. He is "friend-zoned" to the max, the guy even takes a BATH with him despite them both being gay and hugs him PLATONICALLY... WHILE THEY'RE NAKED... Idk if "friend-zoned" is a strong enough description, he's mega friend-zoned. It wasn't till Hayato literally mounted Kazunori that things turned sexual in Kazunori's mind. He's trying to take advantage of his virginity to turn their relationship sexual, he acts super sensual and says sexy things to get that virgin fired up.
Jesus Christ mother of apes, if you needa fuck him why not? just use a banana in stead you fucking whore. If you are gay then say it you dont need to be so dramatic, if you are then you are, not like I am sparking hate for people like that but fuck just shut up about big dicks, that is something so little, like '' OH MY GADD, HE HAS A DICK SO HUGE ITS THE SIZE OF A GOLF COURSE!'' like bruh I think u mean those plastic things made cheaply as childrens toys.