This might not even be his power. He just likes showing up and snarking. And he seems intent on presenting himself as the charmingly rougish and reasonable one of the Demiurges to the Rising Heir. Which might well work as long as Allison never actually sees his realm or his real body.
Edit: also, the textbox "final lesson" makes me think this might actually be a regular occurence. Maybe he's dream-teaching her regularly? Given that the alt-text speaks about his mastery of sword law, which makes sense if he's the current General of the Middle Army, maybe he's actually given her weapons training.