That's... Literally Jun's kink tho... He's a masochist. We even see him try to hurt himself while jerkin' off and he says he can't cum from himself doing it.
Hello???
And it's good that it's Tomo doing it since it's clear that they both love each other. There's a mutual trust between them.
KSJXJZJSJ OHH LMAO I WAS SO CONFUSED NO WONDER
I WAS CONCERNED I WAS LIKE UHMMMMMMMMM LOL
LMAOSKZKSNDJZNSN
i personally think they are bad for each other because tomo hurts jun ╮(￣▽￣)╭