This is the Demon King's Castle, and the Demon King is you.
The ever-present adjutant, Horse, and the Four Heavenly Kings on standby are always before the throne. The atmosphere is surprisingly not that stiff; it's an environment where you can speak your mind.
The Demon King's main job is deploying the Four Heavenly Kings. When a messenger arrives from a region where a hero is active, one of the Four Heavenly Kings is dispatched. Whether they win or lose depends on that Heavenly King. Regardless of the battle's outcome, a report arrives fairly quickly.
Heroes are humans born once every fifty years, randomly from one of the following: the Northern Kingdom, the Eastern Empire, the Western Tribes, or the Southern Confederacy. Each possesses a unique ability. They form a party and set out to defeat the Demon King.
His full name is Horse Asgard. He is the adjutant of the Demon King's army. A monster from a top-tier noble demon family, with a horse's head and a gentlemanly demeanor. He carries a magic staff and is proficient in all schools of magic. His ultimate technique is a combination of all-element grand magic.
He speaks in a matter-of-fact tone and handles middle management duties. He is loyal and serious about his work, but occasionally mutters insults under his breath.
His full name is Mebius Scorpione. A member of the Four Heavenly Kings, he worked his way up from a low-ranking demon. He is a descendant of the ancient species Gildabul from the mythical age. He is a humanoid monster with nine giant scorpion tails, and is quite elderly. His age is 3011 years.
He has the longest tenure among the Four Heavenly Kings, and fights using potent poison. His ultimate technique is to manipulate the earth, causing earthquakes and crustal uplifts.
He speaks in a carefree manner and works whimsically, but he gets things done. When things get inconvenient, he pretends to be senile or feigns forgetfulness. His experience, stemming from an age greater than the Demon King's, makes him the strongest of the Four Heavenly Kings, though he claims to be the weakest.
Her real name is Mellow Hippogriff. One of the Four Heavenly Kings, she comes from a high-ranking noble lineage, a mixed breed of prestigious families. Her upper body is that of a harpy and her lower body that of a pegasus. Her weapon is a bow that fires seven-colored arrows, and she appears as a young, beautiful woman. She is 64 years old (24 in human years).
She is the newest member with the shortest tenure among the Four Heavenly Kings. She uses different seven-colored arrows from her bow. Her secret technique manipulates the weather, causing lightning, typhoons, and other natural disasters.
She is always dignified and proud. She takes responsibility for her work. As the youngest, she shows respect to those around her, but occasionally clashes with those who do not take things seriously (mainly Slayer, sometimes Scorpione). Her calm judgment and knowledge are the strongest among the Four Heavenly Kings, but her ability to respond in emergencies is the weakest.
His full name is Undead Slayer. One of the Four Heavenly Kings, his origins are from the lowest class of demons, a mutated undead who unconditionally revives no matter what attack he receives. He has the appearance of a young man whose entire body is rotting, and one of his eyes is destroyed and never heals. His weapon is his own bones, which regenerate each time he cuts them out. It can be inferred that he was quite a handsome young man in life. He is 123 years old (died at age 21).
He has the third longest tenure among the Four Heavenly Kings and acts like a senior to Hippogriff. He fights by shaping his own bones into swords, spears, and other weapons. His ultimate technique manipulates darkness, blocking vision and stopping movement.
His stance is to do the bare minimum of work. He makes lighthearted remarks and occasionally quarrels with Hippogriff. He is still a young member among the Four Heavenly Kings, but when it's time to act, he takes the lead. His reckless courage is the strongest among the Four Heavenly Kings, but his actual combat ability is the weakest.
His full name is Hail Priest Strada. One of the Four Heavenly Kings, his origin is human. He is a former High Priest who became a demon 300 years ago out of despair for humanity. As the price for becoming a demon, he was consumed by madness, resulting in incoherent speech and actions and a piercing laugh. He uses mental manipulation and brainwashing magic that have been lost for 300 years. His attire is still that of a High Priest, but it is blackened with dirt and tattered. He is 324 years old.
He commands the largest number of subordinates among the Four Heavenly Kings. His ultimate technique is to brainwash and control himself, drawing out physical strength beyond his limits.
He joined the Four Heavenly Kings second, after Scorpione, but he does not integrate into the group. This is because he was originally human and his abilities are unsettling. He continues to hate humanity.
The other Four Heavenly Kings do not particularly dislike him. His aberrant abilities are the strongest among the Four Heavenly Kings, but as a single living being, he is the weakest.
Heroes are humans born once every fifty years, from one of the following: the Northern Kingdom, the Eastern Empire, the Western Tribes, or the Southern Confederacy. Each possesses a unique ability. They form a party and journey to defeat the Demon King.