"It's certainly possible. Sudou, the JOKER killer, held sway over veritable swarms of them. Then again, he was but a pawn of an elder god, so that may not be the extent of an average human. Whether or not traditional devil summoners can contract multiple demons....they might? I think it depends on the summoner's skill. Let the record show I'm postulating here. I really don't know."

It's not something Katsuya's given a lot of thought to, before now.