As a lifelong poly person the concept of NTR never made much sense to me. That, and I don't speak Japanese ;)
Maybe we could get better clarity by using English terms...
cuck: MC is cucked by NPC, whether or not MC is present
bull: MC cucks NPC
rival: MC has to win the affections of an LI from...
I tried to play it a couple years ago. Yeah, good renders, good production, but couldn't identify with any of the characters. You get rewarded for either being a total dick or a total milquetoast but penalized for anything in between. There doesn't seem to be a valid path for an ethical horndog...