Mills, born into a great family, was not the sort of simple-minded playboy who loses his way at the sight of a beautiful girl; despite appearing to be a flirtatious womanizer, in reality, the true him... was scheming and deep, always quietly accumulating power.
He recruited those extraordinary individuals with diverse personalities, considerable strengths, and who carry certain missions, like her, and the other few in this compartment, fitting such a description.
Being able to recruit and even trust these people, Mills must be more than just a young noble with a bit of background to earn their allegiance.
However, having been by Mills' side for so long, it was her first time seeing him drunk by a girl's wine.
Has Mills' vigilance lowered?
No, it's not that Mills' vigilance has lowered; it's that there's nothing about this girl that warrants their caution.
Her eyes are clear and pure, her presence clean, and every movement of hers manifests an inherently harmless nature.