Everyone shits on Harada so much for being dark but honestly her work is art lol. You’ve probs read it but Ike Reibun is pretty good at that, Kobi no Kyoujin follows that a bit (although only for the first volume or so) There’s a pretty good thread about this on Baka Updates :) so you could reference that.
Stigma. One of the guys who raped the uke smashed a whiskey glass on his back and he bled. That sadistic for ya?
There are a couple Gintama did she did that are amazingly sadistic
https://myreadingmanga.info/paraiso-harada-gintama-dj-yami-otoko-eng/
https://myreadingmanga.info/paraiso-harada-gintama-dj-mienai-kusari-eng/

Like SM Gokko or Caste Heaven. Or anything like that of Harada, Psyche Delico, Ogawa Chise etc.
Basically, I want the seme to be sadistic as fuck. ^.^