I don't know what you have in mind, but I recommend that you make the NTR avoidable even for LIs that players don't give points to: Possibly there will be LIs that players who want a harem ending don't like, and even if they don't give them points, They won't want NTR with them either.
In any case, it's simply a recommendation. As I said before, it's actually game over for me the moment we find out that the girl with wich the MC had sex on the plane has been killed. Although possibly any other type of blackmail would have also greatly cooled any type of interest in the game for my part. Personally I don't like the MC being blackmailed very much, but I like the way it's done in the game even less. One way or another, the only way I can see the blackmail ending is with the blackmailer dead at the hands of the MC and if possible after torture that has physically and mentally destroyed the blackmailer. And with the MC keeping everything that belonged to the blackmailer.
In my opinion, starting the game by blackmailing the MC like that can be very good for an NTR game, but I don't think it will attract too many people who like harem games. In fact having the MC be blackmailed into a harem game is, in my opinion, a terrible idea. As I say, for an NTR game it's great, for a harem game it's not particularly rewarding... Unless you can achieve the aforementioned objective in basically the next update in which the blackmail is introduced (or even better in the same update )