Basara Toujou is the central character of his story, a high school student who carries the weight of a traumatic past and an extraordinary lineage. Originally a promising and gifted member of the Hero Clan, his life was shattered by a tragic incident five years prior to the main events. During a crisis, his unique and dangerous ability, Banishing Shift, spiraled out of control, resulting in accidental deaths and widespread destruction within his own village. Although his actions were a desperate response to an out-of-control ally possessed by an evil spirit, the aftermath led to his psychological scarring and, along with his father Jin, his formal exile from the clan.

On the surface, Basara presents a calm, relaxed, and composed demeanor, often maintaining his composure even in awkward or potentially dangerous situations. He is fundamentally compassionate and holds a deep, unwavering belief in the concept of family. However, beneath this gentle exterior lies a more complex personality shaped by his past trauma. He is haunted by nightmares of the village disaster and carries a profound sense of guilt and responsibility, which fuels his primary motivation: to protect those he cares about at any cost. This drive to shield his loved ones is absolute, and when they are threatened, he sheds his usual restraint to become a brutal and relentless opponent, showing no mercy to his enemies. He is also noted to have a keen strategic and tactical mind, often thinking several steps ahead in combat situations.

His role in the narrative is established when his father, Jin, returns from a trip with two new stepsisters, Mio and Maria Naruse. Unbeknownst to Basara, Mio is the daughter of the late Demon Lord, making her a target for various demonic factions seeking to usurp her power. After initially reacting with hostility upon discovering their true natures, Basara's protective instincts take over, and he vows to defend them as his new family. This commitment is cemented by an accidental reverse master-servant contract created by Maria, a succubus, which makes Basara the master. This contract not only binds their fates but also includes a curse that punishes disobedience with aphrodisiac effects, creating a complex and intimate dynamic that requires physical contact to resolve. This pact system later extends to other key allies, such as his childhood friend Yuki Nonaka, as a means to bolster their collective strength against growing threats.

Basara's key relationships are the core of his character arc. His bond with his father, Jin, is incredibly strong; Jin gave up his life as a hero to raise Basara after his exile, and Basara continues to view his father as a hero who saved him. His relationship with Mio evolves from distrust and conflict to deep romantic love, with Basara repeatedly declaring his intent to save and protect her. Maria, despite her mischievous nature and tendency to instigate lewd situations to strengthen the group's bonds, becomes a trusted confidante and ally whom he considers precious family. Yuki Nonaka, his childhood friend, is one of the few from his past who never gave up on him, eventually joining his household and becoming a key member of his battle harem. He also forms significant pacts with Yuki's younger sister Kurumi, who initially despised him for the village tragedy but later reverts to calling him "big brother," and with Zest, a former enemy who becomes fiercely loyal to him. Chisato Hasegawa, the school nurse, acts as a mentor and reveals herself to be a goddess and a distant relative, later entering a secret romantic relationship with him.

Throughout the series, Basara undergoes significant development, evolving from a guilt-ridden exile into a confident leader and the heart of a forged family. His primary motivation remains consistent: the absolute protection of his loved ones, which drives every confrontation with demonic threats, his former Hero Clan, and powerful enemies like the demon Shiba Kyouichi. This journey forces him to confront his past, master his fearsome powers, and accept the complicated bonds he has formed. By the conclusion of the story, Basara has fully embraced his role, marrying the multiple members of his extended household, including Mio, Maria, Yuki, Zest, and Chisato, all of whom bear his children. This outcome symbolizes his complete transformation from a solitary outcast to the patriarch of a new, united family built on mutual loyalty and protection.

In terms of abilities, Basara is a formidable combatant classified as a "Speed-Type" hero, specializing in extreme speed and rapid, unpredictable attacks that can overwhelm even opponents with precognitive abilities. His primary weapon is the cursed demonic sword Brynhildr, which materializes from a pendant and is said to house an ancient, malevolent spirit. His signature technique is Banishing Shift, a terrifying power he inherited from his father. This ability allows him to nullify any attack, magical or physical, by sending it into a zero-dimensional void where it ceases to exist. At higher levels, this power can erase a living being's existence entirely. Due to his unique conception involving a hero father, a demon mother, and a goddess as a surrogate, Basara carries the blood of heroes, demons, and gods, making him an unprecedented "Quadruple Red" being. This mixed heritage, combined with the master-servant contracts that grow stronger through emotional and physical bonds, gives him access to a vast and continually evolving arsenal of powers, including gravity manipulation and enhanced regeneration.