What is meant by NTR (Netorare) is infidelity to sexual intercourse. is it good if we take someone's mother or lover to rape? So in my opinion this is considered NTR because Akane's mother was in a relationship with another man and gave birth to Akane.
you snatching someone's lover to rape is a form of NTR(Netorare). If that happens, then all the women in the story of this game will be owned and fucked by MC, including (Mc's mother)