Hannyabal is a prominent character from the Impel Down arc, initially serving as the Vice Warden of the great underwater prison before eventually achieving his long-held ambition of being promoted to Warden. His journey within the story is defined by a fascinating duality, balancing comedic, self-serving ambition with a deeply rooted sense of duty and surprising resilience.

Hannyabal is a large, pot-bellied man whose appearance is a striking blend of demonic and ancient Egyptian iconography. His face is designed to resemble a Hannya mask, complete with a horn-like brow ridge and a chin shaped like a pharaoh's false beard. He wears a striped nemes headcloth, and his back is adorned with demon-like wings. He is often seen carrying a pitchfork, furthering his devilish aesthetic. Over the course of the story, his attire changes; he initially goes bare-chested to demonstrate his endurance, but after the two-year timeskip, he adopts an outfit similar to his predecessor's, while also having gained a significant amount of weight. His signature weapon is a powerful double-bladed naginata named Kessui, which translates to "Blood Sucker," a weapon he wields with great skill, even spinning it to generate flames for an attack known as the Hanny Carnival: Burning Hell Wheel. Beyond his combat abilities, Hannyabal possesses remarkable physical resilience, capable of withstanding extreme temperatures by walking through the Freezing Hell level in minimal clothing and enduring powerful attacks like Monkey D. Luffy's Gear Second strikes.

Personality is where Hannyabal becomes truly complex. On the surface, he is an extremely ambitious and somewhat comedic figure. He has a notorious habit of claiming ownership of everything in sight, such as declaring "My Impel Down," only to immediately apologize for getting ahead of himself. These frequent Freudian slips reveal his all-consuming desire to become the Warden. His ambition is so pronounced that he is initially willing to jeopardize the security of the prison, scheming to let relatively harmless prisoners escape if it means he can pin the blame on his superior, Magellan, and take his position. He can also be susceptible to the charms of beautiful women, having been tricked by Bon Kurei in disguise. However, this selfish and seemingly unserious demeanor is a facade that crumbles when the situation becomes genuinely critical. When truly dangerous criminals like Crocodile or Jinbe attempt to escape, or when the safety of innocent civilians is directly threatened, Hannyabal's entire personality shifts. He discards his petty ambitions and reveals his true nature as a deeply considerate and heroic individual. He became a gaoler not for power, but to protect the lives of civilians by keeping the world's most dangerous criminals contained. In this state of mind, he displays an iron will and extraordinary resolve, fighting far beyond his limits and refusing to stay down even when near death, a tenacity that has been compared to that of Monkey D. Luffy himself. He does not damn pirates for being rebels, but for the grand crimes they have committed and the fear their very presence would instill in the world's citizens.

Hannyabal's role in the story is central to the Impel Down arc, where he acts as a secondary antagonist and a major obstacle for Luffy and his group of escaping prisoners. His personal journey is one of ironic fulfillment: he desperately wants to replace Magellan, and due to the chaos and failure of the mass breakout, he eventually does. In the past, he was a guard present during the legendary escape of Shiki the Golden Lion. During the main Impel Down arc, he is tasked with guarding a key stairway. Underestimating him, the escapees Buggy and Galdino try to defeat him, only to be easily and effortlessly defeated off-screen. Later, he engages in a serious, all-out fight with Luffy on Level 4. Though Luffy ultimately defeats him, Hannyabal continuously forces himself back to his feet, clinging to Luffy to prevent the escape, until he is finally crushed and knocked unconscious by the invading Blackbeard. In the aftermath of these events, he is promoted, finally achieving his goal and becoming the new Chief Warden of Impel Down.

Key relationships define his interactions. His relationship with his former superior, Magellan, is a constant source of conflict and comedy. Hannyabal openly wishes for Magellan to fail or die so he can take over, often shouting these thoughts aloud before awkwardly trying to rephrase them. Despite this insubordination, Magellan fully trusts Hannyabal, stating that he is the only person worthy of being his successor and is the only other person capable of running the prison. This faith is ultimately validated when Hannyabal succeeds him. He also develops a grudge against the okama Bon Kurei after being tricked and tied up by him. Among the prison staff, Hannyabal is well-regarded and admired for his displays of toughness and his unwavering courage during extreme emergencies. His development is a fascinating subversion of a seemingly petty character, revealing that beneath the self-serving ambition lies a heart of a true hero dedicated to justice and the protection of the innocent, making him one of the most unexpectedly principled figures in the series.