karkat could benefit off a d/s relationship. being someone’s sub would give him focus and teach him discipline. carrying out orders and receiving due punishment would keep him humble.
kankri, as a dom, would finally have the undivided attention he always craved. since he already regards karkat as his pupil, taking him on as his sub wouldn’t really be so unrealistic.
not to mention a d/s relationship doesn’t have to be sexual.
of course kankri could reward his dear little student accordingly without personally indulging himself and endangering his vow.
but there’s an undeniable appeal in karkat leaving his buddies to go see kankri, and maybe he’s late and kankri does not tolerate tardiness.
and his friends, none the wiser, would go, “so what if you’re late? keep the loser waiting” but karkat’s cheeks rouge and he can already hear the spankings he’ll be counting out for every minute he’s late.
and the anticipation of it churns his gut in actual excitement.