NTR Type A ( consensual sex )
The Girl Knows she is cheating and gets pleasure out of it.
NTR Type B-1 ( Manipulated-consensual sex )
The girl does not want to have sex, but the bad guy Black mails, manipulates or other wise tricks her into it, and after a while she starts enjoys it thoroughly.
NTR Type B-2 ( Rape-Till consensual sex )
The girl does not want to have sex, but the bad guy Rapes her constantly Until she comes around to loving it.
NTR Type C (Watching your significant other get raped)
This is barely NTR, this kind is purely watching the girl you like/love get raped in front of you while you are helpless to stop it.
NTR Type D (Loving from afar)
This NTR never establishes a romantic relationship with the girl. She lives her life normally being a friend, co-worker, or not even knowing the main character. She might know he likes her, but she is not interested and loves someone else. This NTR is derived from watching her be with another man while she has unrequited feelings, still triggering the NTR feelings inside the main character as he feels she is cheating on him in some way even though rationally she is not. This version can include Type C but the difference is she does not love, and is NOT interested in the Main Character. If the girl ends up liking the main character over time, or always liked him but never told him, and the scenes in question from her perspective have her thinking or feeling like she is hurting the Main Character in some way even though they are not together romanticly, then that is Type A and not type D as the girl is in some way in her heart Cheating on the Main Character, and is therefore Type A
NTR Type VN (Intentionally Manipulated-consensual sex) or (Voluntary NTR). This one is in the grey area of NTR riding the fine line between it and Netorase. This is where the protagonist deliberately manipulates the situation to get his girl (who would never do it originally and is faithful) to Cheat on them. This is usually facilitated by the Protagonist pushing the girl away a bit and putting them into situations where they would cheat or Get NTRed. All orchestrated by the deliberate actions, or inaction's of the Protagonist. The major difference between this and Netorase is the Feelings behind the Event. The girl is honestly Betraying the Protaganist and has no idea he knows or wants it, so the Protaganist is getting off on the Betrayal and Corruption of the once Faithful Girl, which is the primary feeling behind NTR.
