Cao Cao is a central antagonist who appears in the anime High School DxD Hero as the charismatic and formidable leader of the Hero Faction, a subgroup of the Khaos Brigade that opposes devils, fallen angels, and other supernatural beings. He is introduced as a young, handsome man with short black hair, often dressed in a combination of a traditional Japanese school uniform and ancient Chinese attire. His appearance and demeanor are carefully controlled, reflecting a deep-seated belief in his own destiny and superiority. Central to his identity is his claim of being a direct descendant of the legendary Three Kingdoms period hero of the same name, a heritage he uses to justify his actions and rally followers to his cause.

Cao Cao's personality is a complex blend of charisma, manipulation, and profound arrogance. He is a natural leader, capable of convincing other Sacred Gear users to join the Hero Faction either through genuine persuasion or outright brainwashing, demonstrating a pragmatic and ruthless side to his ambition. He firmly believes it is his responsibility, as a hero's descendant, to eliminate beings like devils, dragons, and fallen angels, whom he views as inherent threats to humanity. This conviction fuels his cockiness; he frequently boasts about his own power and mocks weaker opponents. However, beneath this confident exterior lies a calculating and obsessive genius. Cao Cao is a peerless tactician and a master of psychological warfare, always studying his enemies to find and exploit their weaknesses with cold efficiency. Despite his arrogance, he possesses a warrior's respect for those he deems truly strong, such as Issei Hyoudou, Vali Lucifer, and Azazel, which sometimes influences his decisions on the battlefield.

His motivations are deeply rooted in a traumatic past. Born in a remote Chinese village to a family of farmers, his life changed forever when he awakened the True Longinus, the most powerful Longinus sacred gear, while fighting a monster. Instead of celebrating his gift, his parents attempted to sell him to interested parties, forcing him to flee his home. This betrayal cemented his belief that he could only trust in his own power, specifically his holy spear. After learning of his parents' eventual suicide, he hardened his resolve, adopted the name Cao Cao, and set out to form the Hero Faction, seeking to create a world where humans, particularly those with sacred gears, are not at the mercy of the supernatural.

Within the story of High School DxD Hero, Cao Cao serves as the primary orchestrator of the conflict in Kyoto. He is the mastermind behind the kidnapping of the Youkai leader Yasaka, intending to use her to open a door to the Dragon God's realm. His role in this arc is to demonstrate the immense threat that a highly skilled human with a god-slaying weapon can pose. He systematically dismantles the strategies of the Gremory group and their allies, not through raw power alone, but through superior tactics and his ability to neutralize their abilities. His key relationships are largely adversarial, defined by his rivalry with Issei Hyoudou. He sees Issei and Vali as the ultimate test subjects, powerful dragons in human form whose potential he is fascinated by and determined to surpass, which ultimately leads to his downfall when he prioritizes this test over finishing them off.

In terms of development, Cao Cao initially appears as an unshakable and arrogant villain. However, his defeat by Issei, where his ultimate attack fails because the will of God within his spear favored Issei's dream over his own ambition, serves as a critical turning point. This loss forces him to reevaluate his path. Following his return from the Realm of the Dead, a changed individual emerges. He shows a willingness to cooperate with his former enemies as part of the DxD team against greater threats, such as the Qlippoth faction and the Evil Dragons. He begins to question the very definition of a hero, admitting that his past actions were those of a villain and showing genuine remorse. He takes concrete steps to atone for his past, such as sending money to repair the cities his faction destroyed, demonstrating a significant shift from a self-centered conqueror to a more reflective and even altruistic figure.

Cao Cao's most notable ability is his possession of the True Longinus, the spear that pierced the side of Christ. This holy relic is so powerful it can kill gods and drive believers mad just by looking at it. He wields this spear with unmatched skill, having honed his spearmanship entirely through self-taught experience. His true strength, however, lies in his exceptional combat intelligence. As a pure technique-type fighter, he can predict his opponent's movements by reading their aura and devise counter-strategies almost instantly. His signature power is his sub-species Balance Breaker, known as the Polar Night Longinus Chakravartin, which manifests as seven floating orbs called the Seven Treasures. Each orb possesses a unique ability, such as petrifying objects, sealing the powers of female opponents, redirecting attacks, or instantly destroying weapons. This versatile arsenal, combined with his genius-level tactical mind, makes him one of the most dangerous and effective human combatants in the series, a threat not because of brute force, but because of his complete mastery of the art of combat.