That mysterious girl from class 2-B

Another trait of Jon's is that he tends to wish himself into the weirdest situations. If you want to play up the angle of the girl with a secret the girl he is becoming might have wished to be a ridiculously human robot, to be a ninja or have some other awesome secret with the time limit of 'until she wishes otherwise'. Would be a logical way to add a ninja or token monster-girl to the harem.