Tsukasa infiltrates the academy in the past as a transfer student, and starts gathering information on his target. Of course, past Rui is a loner who gets bullied by his peers and wouldn't harm a fly.

When he asks the other students about him they just laugh derisively and call him a pathetic weirdo. They would say his ideas about magic were outlandish and crazy, even heretical. Tsukasa nods in understanding, it makes sense that the future demon king would be creating dangerous magic.