CH 7-8, 11: Mio finds out that buttsex hurts for Shun, and seeks advice to get better at it. Also, why Shun prefers bottoming.
Two straight(???) guys who enjoy being penetrated
Ch. 13: Izumi seeks advice on whether anal hurts or not.
Ch. 15- 16: It hurt (lmao).
Ch. 33.5: Izumi finally tops Ryouma.
Ch 6-7: Two week break from anal due to a colonoscopy. Doctor finds out anyway (lmao).
Issei makes a startling request to his origami obsessed best friend, Kento, asking if he would "please take care of his prostate."
Tomoya consults a massage therapist to cure his impotence. It's prostate massages that end up doing the trick.
Ch 3: prostate massages
Ch 1- 2.5: anal masturbation
Proctologist
An elite school for the sole purpose of learning anal. Amazing.
Harukaze no Etranger