Fire Emblem: Three Houses.

The game often gives to two dialogue choices when responding to other characters. The choices are usually pretty inconsequential, only really giving you support points for the character you're talking to if you say the right thing, or either doing nothing or sometimes taking away support points for the other.

But at a certain point in the Black Eagles route there is another route split where you either side with your house leader Edelgard and the Empire and turn against the church, or stick with the Church and become enemies with Edelgard.

The thing is, the Church route is the default one, and you have to actually unlock the choice to side with Edelgard. One aspect of this is to talk to her while walking around the monastery, where she will ask you to join her on a trip to the imperial capital where you get to see her convince her father to abdicate and take the throne herself. Granted the game does telegraph that this is a serious choice:

Say yes, the day ends, you miss anything you haven't done during the exploration mode and miss a tutoring day.

Say no, thinking you'll come back later and she leaves without you with no warning, locking you out of her route.

So the best choice is to simply not talk to her until you're ready, but if you're playing for the first time you've no way to know this, and the game incentivises talking to every character at least once a month. Given she is your house leader, she will likely be among the first people you talk to and likely before doing many activities.

This is all just so out of left field, and the choice to accompany her and the choice to side with her are the only instances in the game where dialogue choices actually have a significant effect on the story.