Don't worry about him joining that incompetent military. The physical exam was his strong point. With his lack of common sense he will definitively screw the written exam up.
When he decided to NOT break the dummy, because he overthought stuff, I was facepalming me self so hard, I fear it will leave a mark.
Welp, if he isn't accepted, that belt princess will leave, too. And woman in mithril arm, too.
Sadly, from the looks of it, the empire are the bad ones. So joining their military isn't going to happen. And that witch would be in a world of hurt provided by her sensei, if she wouldn't interfere with this development, so...
But I still see a fun, open adventure plot, in which the military chases after them to undo their mistake.