@exebba When he first travelled to this world, he was given "bonus points" that he can use to buy various OP abilities. The people of this world can only ever have one job equipped, but Michio can use multiple jobs at once thanks to his bonus points. He can set up to as many as he wants, but needs the bonus points for them and they get exponentially more expensive the more jobs he equips.
Oh. "Force class" was a good catch. That's a typo - it should be "Fourth Job". It's written kind of weird in the original Japanese.
He can add more bonus points to his "multiple jobs" skill to use more jobs at one time.