Jozak Guriere is a supporting character known for his loyalty and unconventional methods. He is a childhood friend of Conrad Weller, a fellow Mazoku soldier, and eventually becomes a close subordinate and personal bodyguard to Yuri Shibuya, the series' protagonist and the 27th Demon King.

Regarding his background, Jozak is of mixed heritage, being half-Mazoku and half-human. This lineage places him among the warriors of Lutenburg, a group of half-demons who had to prove their loyalty in a significant battle, of which he is one of the survivors. His mother is deceased, and he has a long lifespan typical of his kind, being over one hundred years old, though he maintains the appearance of a man in his mid-twenties. Physically, Jozak is a well-built man with bright orange hair parted down the middle and kept long in the back. He has blue eyes and is often seen in a tattered brown vest over a black short-sleeved shirt.

His personality is multifaceted, combining a shrewd and cautious nature with a light-hearted and friendly demeanor. Initially, he was wary of Yuri becoming the Demon King, fearing that the new ruler might repeat the disastrous mistakes of the previous king, Stoffel. This suspicion leads him to test Yuri's character, demonstrating that he does not trust easily and believes a person must prove their worth. Despite this initial skepticism, Jozak is fiercely loyal once his trust is earned. He is also known for his fun-loving attitude and a unique quirk of cross-dressing as a nurse or a maid, particularly on stealth missions. This habit is more than just a gag; it is a personal superstition, as cross-dressing once saved his life and is therefore considered a good luck charm. His skills as a spy also make him an adept actor, capable of adopting any necessary persona to complete his objectives. He is compassionate and capable of withholding judgment about people even when he harbors suspicions about them.

In the story, Jozak serves as a spy and bodyguard for the Demon King. One of his most significant actions occurs early in the narrative when Yuri, Conrad, and Wolfram are on a ship searching for the legendary demon sword, Morgif. After Yuri inadvertently uses his powers to repel an attack, they are imprisoned, and Jozak, having been undercover on the ship, frees them. Later, he plays a pivotal role in Yuri's acquisition of Morgif. When it becomes clear the sword needs to absorb life force, Jozak tricks Yuri into entering a gladiator-style competition, using the situation as a test to see if the new king is worthy. During the ensuing fight, the power source for Morgif is lost, and Yuri entrusts the precious jewel to Jozak for safekeeping. His role as infiltrator is highlighted again when Yuri is held captive; Jozak dresses as a maid to sneak into the castle and attempt to free him. His dedication to his duty is absolute, as he is even shown being pushed off a cliff by Conrad as part of an elaborate undercover operation to deceive their enemies, confirming his willingness to endure great personal harm for a mission.

His key relationships are primarily with Conrad Weller and Yuri Shibuya. As a childhood friend of Conrad, he shares a long and trusting bond with the soldier, allowing them to coordinate complex and dangerous plans together. His relationship with Yuri evolves from one of initial caution and testing to profound loyalty and service. He becomes Yuri's personal bodyguard and spy, and Yuri affectionately gives him several nicknames, including Ms. Biceps, Oniwaban, and The Spy. He is a trusted member of the inner circle surrounding the Demon King.

Throughout the series, Jozak shows significant development in his perception of the new king. He moves from fearing that Yuri would be a failed ruler like Stoffel to becoming one of his most dependable and loyal protectors. His initial tests give way to genuine respect and dedication.

In terms of notable abilities, Jozak is unique in that he possesses no magical powers. To compensate, he relies on exceptional physical prowess. He is a highly skilled swordsman, possesses considerable physical strength, and is remarkably agile. His primary talents lie in espionage; he is an expert spy and infiltrator, with acting skills that allow him to assume any identity required for a mission. Furthermore, he is a proficient woodworker and is handy with tools, demonstrating a practical and manual aptitude.