Karin has a weakness built into the acceptance of her family and her sister, she clearly hates the fact her sister doesn't give two shits about her because Kirin thinks Karin is too perfect, Karin is not 'adverse to lewd' she simply thinks it's immoral if there's no love involved and she still always needs to be the perfect child. Karin wouldn't have sex with Akira if it was a forced situation unlike the parallel of her sister who woulda just done it right there, Kirin and the love hotel, meeting in the dorm rooms during beach etc, complementing Noriko in the same character ideals that play off each other.
Karin wants love and Husbandry and the entire result of getting married into a wholesome endgame. I think the only ways she breaks this is seeing either Kirin or Her teacher (Wakana?) breaking their bond and enjoying Akira like stuff is alluding to. It's either that or catching Miku? someone else in the act and them Cumming too hard she wants to know what it feels like to be 'bad' type of trope.
We can probably also apply this scenario to touka and some others?
Karin's definitely adverse to lewdness, and couldn't even stomach seeing a girl touch a boy non-sexually:
Karin also seems to have androphobia on top of her innocence and purity.
Frankly, unless she trades her body and morals for her sister, I don't really see how else she'd ever "willingly" be with Sensei, sexually. Especially after what happened. Albeit, if Sensei reinvents himself or gets reinvented, then I could see something happening.
Same; especially when her spring generic events (had to use URM for sneak peek) look so...exceedingly normal. It's almost like nothing ever happened and their dynamics hasn't changed a single bit. What kind of miraculous save does a busted groomer need to retrace his relation with a girl who you almost raped?
Kirin could have a part to play as a degenerate, a siscon, and someone that "perceives" Molly incident, but I am entirely unsure whether Kirin can provide enough push to move Karin's chapter forward; Kanda sisters might have less divide after this, but Karin is currently on such high alert and is smart enough to just let either Sensei or herself close the deep trench now lies between them without some good heart-to-heart; then it circles back to the question "what can possibly be good enough in Karin's eyes under this situation".
I suppose we can always have Karin "corrected" like Futaba by the end of Fish Eyes, but......yea I dunno.
The generics seem a little out of order. Ami's, for example, couldn't happen until at least next update, but they've been prepared for a few updates now. Karin's may have been intended to take place before this one, but wasn't implemented yet.
Although, perhaps Karin will simply be reset, like Maya, and Sensei gets to have a better chance at grooming her? Kirin would probably be the only one besides Sensei that would notice.