The simple answer? Neither.
It's more complicated than that.
Ideally, NTR stands for Netorare, which is when an established love interest/partner is stolen away by another through sex. Literally, "taken away by sleeping with" from the perspective of the person who lost the partner.
Netori is related, but it would be when the activity is done by the MC to a rival.
The current official definition of NTR on F95 is rather weak:
- NTR [Designed to cause jealousy by having the romantic interest involved with someone other than the MC.]
With a definition that broad, it could be someone kissing the LI, it could be someone giving a hug or a massage to a LI. It could even be someone
looking at the LI in the "wrong way," or the LI looking at another.
Causing jealousy is a VERY vague term.
Once again, subjective. Does it evoke jealousy because Richard received a blowjob from your sister (or rather, your sister was orally raped by Richard) before you started perving on her? Does it make you realize what she has gone through, how difficult her life has been, why she's so hostile, inspiring you to treat her better from now on?
What feelings does it invoke to find out your sister had been orally raped? What does that reaction say about you?
I'm reminded of Mike and Alexis in Love and Sex Second Base. For years, he believed that Alexis had cheated on him and dumped her. He finds out in the present she had been raped by a teacher and to add insult to injury, instead of Mike helping her get through the trauma, he abandoned her. When he meets her again, her self-esteem is shot and her approach to sex is toxic in response to her abuse, her PTSD.
How is the MC's sister getting orally raped any different?