Let me guess. Her husband to be will turn out to be a cartoonishly evil jerk, king will ask MC to rescue her and after the climax (lol) she'll rope him into marrying her as well, and the first girl will accept because how could she even dare to monopolize him or some dumb isekai logic.
I haven't read anything besides the manga, but those plot twists are so common that I'd really be surprised if literally anything else happened. Everything always goes the MC's way. God forbid him having to choose between girls unless there's a clearly 'superior' one, and that won't stop the other four or five girls, maybe more, from hanging around him like trophies. The only way other males can hook up with the good girls is if there's already some sort of engagement between them and even then there's no guarantee of surprise NTR from the MC.