NTR doesnt need to be sexual. Well. Sometimes partially.
And it also doesnt need to be NTR to feel the "NTR" vibe.
And it depend if the reader have/had feelings for a certain character.
To say an example :
https://www.novelupdates.com/series/sono-mono-nochi-ni-wn/
Its NTR (despite mods/users keep removing the tag)
Bc the childhood friend with a childhood promise to marry, go with the hero. And start the story of novel.
Now you will get the handpicky jackasses, that will say "naaah its just a promise, they werent together blablabla" but NTR is still NTR (stolen)
Just like the fact, in xianxia, a fiancee being stolen is NTR, "taking lover".
Author won a LN adaptation.
And rewrote that the "childhood friend" slapped the hero that kissed her, and chased MC. And end in MC's harem. +2 new original waifus.
But just like a rewrite, like the rewrite in a good chinese novel where the author had a stroke and wrote a weird ending disliked by all, the readers/fans basically consider the "first itteration" as CANON.
The earlier work of FAIRY TAIL author.
Name : RAVE MASTER
There is a ONEE (ara ara vibe), single forever
Far later, a reformed villain, have his memories shown, and show him going to island and be welcome by the oneesan of MC. Talk together, visit island, etc.
And then bam, show a ecchi scene of...............bed act.
And more classic, can be ANDROID18 from DBZ
Lot of spectators felt NTRed by KRILLIN.
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Btw (warning useless info you will maybe regret knowing)
The fact a dad feel bad that his daughter marry someone. Is kinda NTR feeling. Bc a "woman" belonging to him, is taken away. But just the fact they are related by blood, and normal logic, stop people to understand this. (Incest)
"Its them, NOT ME"
Ntr is such a deep a profund topic that we can philosophy in new eve
Cough, i did
(shower thoughts)
Read this post, to see my pointless but kinda true reasoning.