One of the LIs (futa or not, the player can choose that before begin the game) has sex with someone who ain't the MC and it can be seen or not (it's skippable, not avoidable, you only choose to see it or not, voyeurism would be a missing tag). I haven't played the game yet, I know this just reading the thread...If someone's too purist, that's NTR from the beginning... In many games seems to be that any LI must remain untouched when even there was no relationship to begin with, just because there was 'eye-contact'.. First, the story must begin with something to get along and the DEV choose to begin with this, that's the background so the story leads away.. For me that's good because adds some depth to the story.
I admit NTR only if all the decisions made on gameplay meets to that situation, if you cheated the girl and don't cover right that occasionally that may imply to be cheated because you deserve it so the story acts accordingly and there'll be consequences. I don't play yet any game with such premise, don't remember any..