Silvia remains as adorable as ever here.
And of course there's fine print, no way they'd let it be that easy to just rank up through school events or there would be way more higher ranked staff. Hell, if he got to 6 he'd probably be the same rank or just barely under some of the teachers in the school.
This also explains a little bit as to why we had that whole little beach adventure, to introduce Mephisto into the story so he'd play a role here in king Iruma's founding... That being said, isn't it bad for a student to literally miss a month of schooling at the minimum? Even if it is for a rank up?