Basara Tōjō is the central protagonist of his story, a young man whose life is defined by a complex heritage and a traumatic past. Initially presented as a seemingly ordinary high school student, he harbors a deep and troubled history as a former member of a hidden clan of Heroes. His early life in the hero village was marked by great promise; he was considered a prodigy, having inherited significant talent from his powerful father, Jin Tōjō. This potential, however, was shattered by a catastrophic incident. Five years before the main events, an evil spirit was unleashed, causing chaos and death in the village. In a desperate attempt to protect his childhood friend, Yuki Nonaka, Basara lost control of his unique power, Banishing Shift, which eradicated the spirit and the bodies of the victims, leaving a massive crater in its wake. Though his actions saved Yuki, the village elders held him responsible for the disaster, leading to his and his father's exile from the hero clan. This event left him with deep psychological scars, frequent nightmares of a cloaked man and a crying girl, and a profound fear of his own abilities.

His lineage is extraordinarily rare, being a "Quadruple Red" who carries the blood of four distinct races. His father, Jin Tōjō, is a legendary hero who gained dragon powers by drinking the blood of Fafnir. His biological mother, Sapphire, is a demon lord-class demoness and the sister of the previous Demon Lord, Wilbert. Furthermore, he was carried to term by Raphaeline, a member of the Ten Gods, granting him a divine lineage as well. This unique mix of hero, demon, dragon, and god makes him an irregular being, not fully accepted by any single race.

In terms of personality, Basara typically presents a laid-back, calm, and collected demeanor, often appearing as a normal, if somewhat shy and indecisive, teenager. He is fundamentally good-hearted and possesses a powerful, almost stubborn, belief in the importance of family. This conviction drives his core motivation: to protect those he considers his loved ones at any cost, even if it means fighting against his former allies or taking extreme measures. While he is brave and quick-thinking in emergencies, he can be uncomfortable with the amorous attention he receives. Underneath his reserved surface lies a hidden sadistic streak that emerges in specific situations, particularly in his interactions with the school nurse, Chisato Hasegawa, or when dominating his enemies.

His role in the story is cemented when his father returns from a trip with two new stepsisters, Mio and Maria Naruse. After learning they are demons—Mio being the targeted daughter of the former Demon Lord—he initially tries to distance himself. However, his protective nature quickly takes over, and he vows to protect them as their older brother. This decision leads to the formation of a Master-Servant Contract. Though intended to make him Mio's servant, a mistake by the succubus Maria makes him the master, binding their souls together and linking their powers. The succubus magic used in the contract has a unique penalty: any act of disobedience or disloyalty from his servants triggers a powerful aphrodisiac curse that only Basara can relieve. Over time, he forms similar pacts with several other key female characters, including his childhood friend Yuki Nonaka, her sister Kurumi, the former enemy Zest, and the goddess Chisato Hasegawa.

As a fighter, Basara is classified as a speed-type who overwhelms opponents with blinding quickness and precise sword strikes, a style known as Infinite Slayer. His primary weapon is the legendary demonic sword Brynhildr, which he can materialize from a pendant and which can grant him various forms of magical armor. His most iconic and feared ability is Banishing Shift, a power he inherited from his dragon-blooded father. This technique allows him to send any physical or magical attack, or even matter itself, into the "zero dimension," effectively erasing it from existence. This power is tied to his spiritual balance and, due to the trauma of his past, he initially placed subconscious limiters on it, only unleashing its full potential in extreme situations. He also possesses the superhuman strength, durability, enhanced healing, and magic resistance common among heroes, all of which are further amplified by the Master-Servant Contracts he holds.

Throughout his journey, Basara develops significantly from a guilt-ridden boy afraid of his own power to a confident and formidable protector. He confronts a wide array of enemies, from the current Demon Lord's faction to corrupt heroes and even gods, all while navigating a complex web of political intrigue. He forges crucial alliances, such as with the demon Lars, and his relationships deepen as he learns to trust his growing family. His resolve to protect his loved ones expands beyond his initial circle, and his journey culminates in him leading the charge in an interdimensional war to secure the future of the demon realm. Ultimately, his story is one of overcoming a traumatic past to embrace a unique destiny, forging unbreakable bonds with those he has sworn to protect.