I'm honestly surprised how rare this was. Didn't particularly care to seek it out but it is something that would be interesting to see more of.
Not OP, but I would be interested in this. Generally fine with futa but rarely find the actual art execution of futa games/hentai to be all that appealing. Only one that really comes to mind is something Dine & Dash but that's more just straight futa and not NTR. Just a game focused on futa that happened to be appealing to me.
Best example off the top of my head is
[Infidelisoft] Building our Futature
Where you play as a futa stealing a married woman from her husband. A lot of hardcore BDSM though might be off putting check out the gallery first before deciding to play.
In both TiTs and CoC not CoC 2 had a lot of bad ends where you get cucked by a futa if you play as a man and your female companions get taken from you.
[Mille-feulle] Mezameru to Itoko wo Mamoru Bishoujo Kenshi ni Natteita | After Regaining Consciousness I Became My Cousin's Bishoujo Guardian Swordswoman
I am pretty sure this counts as while the MC is female a lot of the game their girl friend or girlfriend to be is taken from them by the futa antagonist who then goes on to enslave both of them. Not ideal but again this is slim pickings and does count as the MC returns to being male in the canon ending. Female antagonist is the silver haired futa with horns.
[TinkerBell Bougumi] Yumekoi Tensei
This isn't futa but lesbian NTR as while pushing it should count technically. Basically Male MC triggers a reincarnation of female who longs for the male reincarnation of her lover. The two are pretty much fated lovers and the canon couple of the game. The female childhood friend in one route helps the former male MC fight against his feeling for his new boyfriend and they end up together instead as shown in this picture.Therefore you can argue the former male MC's female childhood friend NTR'd the fated reincarnated male lover, who the former Male MC is destined to be with. This is really pushing it though as the childhood friend is more of love rival than antagonist. This gives you an idea how little content there is.
[Crowd] Yin-Yang! X-Change Alternative
Another lesbian NTR technically but not an antagonist doing it. Basically as a former male you accidently manage to cuck one of your best male friends as one of the alternative endings to his route. Basically he got greedy had a 3some with you and his girlfriend as a competition to help decide who was best suited to be with him. During sex depending on what options you pick his girlfriend ends up leaving him for you. This is mostly played for laughs unfortunately as it would have been great to have a final sex scene with the girlfriend. It is the picture with the red head.
[Crowd] X-Change 2 R
This is futa NTR but pushing it for 2 reasons The futa is at the end of the route and most of the NTR action is off screen. It is mostly Lesbian NTR against another woman rather than man. It isn't until the end the former male MC finds out because he now she had been ignoring his girlfriend she became addicted to the step sister's dick which was created by the formula that would have changed the MC back. However since its from the player's point of view you don't know this until the final scene of the step sister route. However while it never outright says it in the game. It is heavily implied the step sister was using the MC's girlfriend to make the MC hers as she prefers him as a female and stole the formula that would change him back. Also the MC is pretty into their step sister at this point and it seems that both the MC and their former girlfriend are more interested in stealing the step sister away from each other. Until the step sister makes them behave and made them both her loyal girlfriends.
Also to be clear it has to be the version with R on the end. The original game didn't have the step sister route and its my favorite route as its pure yuri/futa unlike the step sister route in the other games. Lots of types of NTR in this game as canonically the mc has gf in 2 and 3.
I will try and find more sorry for the spoilers but the context was needed in this case to explain how they can be counted as NTR. Also my memory isn't 100% accurate it has been a while for me. I am still not adding everything and don't get me wrong all the games are pretty sexy with their scenes even if it doesn't meet the critiera exactly.
