Being a smart student, it certainly shouldn't have surprised Jun that he'd be accepted for a programme that gave the school a chance to show off their work. That is to say, if he actually did sign up for the programme... which he didn't.
This ultimately left only one possible explanation. One that the magus in training was all too happy to bemoan in his mind: "Riko-nee."
Synopsis: Jun is signed up for a student exchange program as a prank by Riko. He ends up going to Koza high school, Okinawa where he gets involved in strange movements from vampires, a secret organization and even the U.S army
Curbstomp Battle: When Kai tries and utterly fails to fight Jun in a fit of anger for being left out of the operation. It's stated that he would have met the same result trying to fight David, who was his original target.