Welcome To Demon School, Iruma-Kun! is about Iruma, who has to learn how to cope with demons at Babyls while concealing the fact that he is a mere human. Students at the Demon School are taught how to use Bloodline magic and how to survive in the Demon World by the world's most prestigious professors. Among the lessons, Kalego teaches students that summoning a Familiar is an essential step to surviving in the Netherworld.