I don't mind the fiancée as a character, but as a narrative development it's a bit too convenient imo.
MC was stuck between a rock and a hard place with the minister now forcing him to take on his own accidental army and the introduction of a fiancée whose motivations are unclear could've made for a bit of intrigue and character development (finding out whether she's an ally or has her own ambitions, whether she can be trusted, etc) but instead she conveniently cast Infinite Surveillance on him years ago and is not only fully aware of his situation but supports him on top of that, and supposedly all because he made for an interesting subject for research.
This is starting to turn into Teihen Ryoushu no Kanchigai Eiyuutan with how quickly the mc is surrounding himself with competent underlings/allies who force him on a path to power.