Iruma Suzuki, a fourteen year old Japanese boy incapable of refusing polite requests, works hard to support his scumbag parents. He is suddenly kidnapped to the Netherworld by the demon Sullivan after Iruma’s parents sold his soul. Sullivan wishes to adopt Iruma as his beloved grandson, since his friends Levy and Belial always boast about their grandsons and he is jealous. Iruma agrees and is enrolled in Demon School where he must keep his human identity secret or risk being eaten by his classmates. Iruma attends opening ceremony and learns Sullivan is the schools director. First Year Representative Asmodeus Alice tries to give his speech but Sullivan makes Iruma do it instead. Iruma reads a speech provided by Sullivan, terrifying and impressing the students as the speech was actually a dangerous spell to prevent Iruma falling or embarrassing himself. Asmodeus challenges Iruma to a duel for insulting him but Iruma, having been raised by scumbag parents who constantly put him in dangerous situations, has developed an almost superhuman ability to dodge out of the way. The other students assume Iruma refuses to fight back because he considers Asmodeus weak. When a girl in the audience is almost hurt Iruma saves her, but the effects of Sullivans spell prevents him falling forwards and he accidentally knocks Asmodeus unconscious by throwing him backwards in a German Suplex. The story spreads throughout the school, making Iruma famous. Iruma is shocked when Asmodeus happily declares himself Iruma's servant. Sullivan is delighted Iruma seems to have a bright future in the Netherworld.

During breakfast with Sullivan Iruma demonstrates his ability to consume truly shocking amounts of food. He tries to refuse to attend demon school but decides to go when Sullivan reveals he has bought even more thoughtful gifts for him. Asmodeus informs Iruma they must summon their magical familiars and the strength of the familiar will determine their demonic rank and which class they are placed in. Their advisor, Naberius Kalego, immediately dislikes Iruma for being Sullivan’s grandson. To summon a familiar the students perform a ceremony using their blood on summoning parchments marked with Naberius' demonic seal to prevent cheating. Asmodeus summons a fire breathing Gorgon snake. Iruma tries a summoning but as he has no demonic power in his blood the familiar summoning accidentally becomes a demon summoning using the power of Naberius' demonic seal, causing Naberius to be summoned as Iruma's familiar in the embarrassing form of a small, cute, fluffy owl with bat wings and horns. Despite it being an accident the other students assume Iruma must be even more powerful than Naberius to be able to bind him as a familiar, thus increasing Iruma's fame even more. Sullivan happily informs them familiar summoning contracts are unbreakable and last an entire year. Naberius becomes bedridden from shock and Iruma's rank is left undetermined. Iruma meets a hyperactive student named Valac Clara whom Asmodeus warns Iruma not to speak to.

Asmodeus explains Clara is a weirdo who people try to avoid. Clara becomes attached to Iruma who is compelled to play with her after she says "please". Clara reveals she possesses magical pockets which can copy any object she sees. Iruma learns other students have been manipulating Clara into creating free food for them. Clara sadly reveals she has gotten used to having to bribe people to be her friends. When she tries to bribe Iruma he refuses, upsetting her, until Iruma explains he wants to be her friend without bribes. This makes Clara so happy that when the other students try manipulating her again she throws a drinks machine at them before using Asmodeus as a target for paint dodge ball.

Iruma is unsure if Asmodeus and Clara are his friends since he never had friends before. Iruma learns a student's rank controls what food they can order. Clara gets in trouble with the snack stall owner who considers her replicating pockets a form of shoplifting. Naberius arrives to settle the matter only for Clara to trick Iruma into summoning Naberius, turning him back into an owl. Iruma, Clara and Asmodeus flee while the stall owner traps Naberius and demands payment for the shoplifted items. Iruma asks Asmodeus and Clara if they are his friends but is surprised to learn demons have no concept of "friends", but they agree to be friends anyway. Sullivan holds a faculty meeting where it is decided Iruma, Clara and Asmodeus will all be placed in the Misfit Class for Problem Children.