Its a japanese term known as Netorare or Netori(but netorare most of the time) (though both have somewhat same meaning but different wholely)
NTR is an abbreviation of the word "netorare". It's a genre of Japanese porn in which someone's partner is stolen from them sexually; it may or may not involve ending the relationship but the partner derives sexual pleasure primarily from someone else. By extension netori is when a protagonist steals other people's sexual partners. However, people here on this site use the term in a way I'd never even heard of before coming to this site-in which any female character in a story or game engages in any form of sexual contact with a male character that is not the protagonist in the game or story. I'd rather not even classify that as a valid definition but I am defining it because you will see it used that way on this site, often times in violation of the site's rules against fetish bashing.
Ah thank you, i don't know these terms that well.
The antagonist suggests that MC do his French homework for him, MC struggles somewhat to refuse. As for the sister, it could be blackmail, maybe, but the narrator's description seemed to me to imply mind control more. We'll see what's going on eventually, I guess.
C'mom let's be a bit less lazy. You just need to read a couple of previous pages to find it.
