"Welcome to Demon School, Iruma-kun" centers on Iruma Suzuki, a 14-year-old human boy who is sold to a demon by his neglectful parents. The demon, Sullivan, is a high-ranking figure in the Netherworld and adopts Iruma as his grandson. To protect Iruma from the dangers of the demon world, Sullivan enrolls him in Babyls Demon School, a prestigious institution for young demons. Iruma must navigate this unfamiliar environment while concealing his human identity, as humans are considered a rare delicacy in the Netherworld.

At Babyls, Iruma quickly attracts attention due to his unique circumstances and Sullivan’s influence. Despite his initial fear and lack of demonic abilities, Iruma’s kind-hearted nature and resourcefulness help him form friendships with his classmates, including the ambitious and fiery Asmodeus Alice and the mischievous yet loyal Clara Valac. Asmodeus, initially skeptical of Iruma, becomes fiercely protective of him after witnessing his humility and determination. Clara, on the other hand, is drawn to Iruma’s kindness and becomes one of his closest companions.

The series explores Iruma’s growth as he adapts to the challenges of demon school, which include rigorous academic tasks, magical competitions, and social dynamics. A recurring element is the "Misfit Class," a group of students with unconventional abilities or backgrounds, to which Iruma is assigned. The class is led by the enigmatic and often unpredictable teacher Kalego, who tests Iruma’s resilience and leadership skills. Iruma’s ability to inspire and unite his classmates becomes a central theme as he rises to unexpected prominence within the school.

Throughout the narrative, Iruma’s human traits, such as his empathy and adaptability, set him apart from his demon peers and often lead to surprising outcomes. His possession of the Ring of Gluttony, a powerful artifact gifted by Sullivan, further complicates his journey. The ring, inhabited by the spirit of the demon Alikred, grants Iruma immense power but comes with its own set of challenges and responsibilities.

The story balances comedic and dramatic elements, with Iruma’s interactions with his classmates and teachers driving much of the humor and character development. Themes of friendship, self-discovery, and overcoming adversity are woven into the narrative as Iruma gradually earns the respect and admiration of his peers. The series also delves into the broader hierarchy and culture of the Netherworld, introducing various demon clans, traditions, and conflicts that add depth to the setting.

As Iruma progresses through his school life, he faces increasingly complex challenges, including rivalries, magical battles, and moral dilemmas. His journey is marked by a blend of lighthearted moments and high-stakes situations, creating a dynamic and engaging storyline. The series maintains a focus on Iruma’s personal growth and his evolving relationships with those around him, making it a compelling exploration of identity and belonging in an unconventional setting.