@ss4chris Thx for the direct personal attack, seems like you felt I referred to you while in reality I meant it generally. Whatever.
As an avid NTR consumer I would say this is not an NTR story.
Can't snatch what's not yours. Just like with this story. Redhead in highschool never liked Sung-min (our MC) as she herself thought (as shown in this chapter) she is "stuck" on Hak-chul (teacher's fuckboi). In an earlier chapter she only said she was worried about Sung-min (him being bullied) while the dumb MC confessed because he though she will do that too. In any NTR story it is estabilished that the FMC and "the MC" are mutually in love, which is the whole concept of NTR.
So the fact that she was later taken from Hak-chul by the MC (Sung-min) makes this at best only a netori story (depending on the time and story of when and how she was welcomed by our BJapaneseC MC), not an NTR one.