This is a very profound question, and I believe answering it represents true cultural exchange.
As a Japanese person who understands the fascination with NTR, let me share my analysis.
NTR is currently the most popular adult genre in Japan. When something becomes the most popular genre, even in adult content, it always reflects social conditions and the current state of society.
In modern times, Japanese men have lost much of the strength their predecessors possessed. Yet they are still often expected to demonstrate traditional masculine strength. This creates anxiety and pressure for men.
When a man cannot maintain an erection with someone they love, it's usually because they're overwhelmed by this anxiety and pressure. To perform sexually, men need to summon their masculinity. This also explains why some men can masturbate but cannot perform during actual sex.
Men fear directly telling their loved ones they 'cannot have sex' because they worry this admission might strip them of their masculinity. Japanese people believe that feeling pathetic destroys masculinity. Therefore, Japanese men are constantly troubled and exhausted by this pressure.
However, what happens if someone who is more masculine suddenly appears and takes away their loved one? While having a loved one stolen is painful, from another perspective, it forcibly releases men from their anxiety and pressure. The key point here is that it's 'forcible.'
By becoming a victim, they can maintain their legitimacy. In other words, they can claim they didn't voluntarily abandon their masculinity.
The recent popularity of novels about 'being forcibly expelled from one's organization' in Japan might stem from the same reason. Release from masculine responsibility directly leads to catharsis.
Only after being violated by another can they achieve an erection with their loved one in a relaxed state. Japanese men desire release from pain and stress more than being strong themselves.
What do you think?