Beelzebub, also known as Beelzebub Yuichi, is a demon who appears in the anime You're Being Summoned, Azazel Z. He is a high-ranking demon from an elite aristocratic family in Hell, embodying the sin of Gluttony. In the human world, his appearance is deceptive: he looks like a small, formally dressed penguin wearing a crown, a stark contrast to his monstrous true form which is that of a gigantic fly. This cute, bird-like guise is a result of a spell cast by the demon detective Akutabe on his office, forcing all demons within to adopt a harmless, chibi-like form.

Despite his regal and polite demeanor, Beelzebub's personality is a grotesque contradiction. On the surface, he is well-mannered, articulate, and seems to be the most cooperative and intelligent of the demons working for Akutabe. However, this refined exterior masks a deeply depraved nature. His most defining and repulsive characteristic is his appetite for feces, a trait befitting his title as "Lord of the Flies". He treats his scatological diet as a sophisticated hobby, even defending it with an eco-friendly philosophy of "self-recycling". His personality can swing from courteous and sarcastic to violently crude, and he harbors a strong sense of superiority due to his noble birth and elite education, looking down on lower-class demons like his rival, Azazel.

Beelzebub serves as one of the demonic assets for the detective agency. He is initially bound by a contract to Akutabe but is later transferred to the assistant, Rinko Sakuma. His role in the story is to use his unique abilities to help solve cases, though his methods are often as problematic as the problems they are meant to solve. His primary ability is the power of "Exposure" or "Revelation". This allows him to forcibly draw out a person's hidden true nature, secret desires, or embarrassing truths. The most prominent and comedic application of this ability is inducing uncontrollable defecation in his targets, an attack that is both humiliating and powerful. He can also enhance this ability by consuming specific offerings like goat dung, which acts as a performance-enhancing catalyst.

His relationships with other characters are central to the comedy. His most significant dynamic is with Azazel, a lazy and perverted low-class demon. They share a long and complex history as childhood friends and classmates, but their relationship is defined by rivalry and mutual disdain. Beelzebub was bullied by Azazel during their school days, a fact he has not forgotten, and he now takes pleasure in his own elevated status and in tormenting his former bully. He is utterly terrified of their master, Akutabe, whose overwhelming power can instantly neutralize any demon, a lesson Beelzebub learned very quickly and violently. Towards Rinko Sakuma, he maintains a contractual politeness, but his underlying obsession with her waste products creates a bizarre and uncomfortable tension. As a demon, he is also occasionally pursued by angels who seek to reclaim his grimoire, a book that is the source of his power and immortality on Earth.

Throughout the series, Beelzebub shows little to no character development in terms of moral growth. He remains a self-serving, elitist, and gluttonous demon whose primary motivations are maintaining his comfortable existence and indulging his revolting appetites. While his contract may change owners, his core personality and his contempt for others remain constant. His power is formidable, as his true form is a massive, monstrous fly capable of battling other high-ranking demons like Lucifer, but he is generally kept in his harmless penguin form by Akutabe's magic. He is, in essence, a perfect example of the series' central theme: a fundamentally irredeemable and disgusting bastard, made all the more hilarious by his pretensions of nobility and class.