Shūichi Natori hails from a family once part of a renowned exorcist clan. The clan retired after generations ceased producing members capable of seeing yōkai. His birth, marking the first resurgence of this ability, prompted his family to view him as a target for vengeful spirits. They blamed him for misfortunes, straining his relationship with his father and fostering a pessimistic, antisocial demeanor in his youth.

As a child, he discovered the injured yōkai Hiiragi bound to a family storehouse. He bandaged her hands and confided his familial struggles. Hiiragi countered his self-perception as a curse, asserting children cannot curse others and that his presence brought her happiness. This encounter left a lasting mark, though they parted ways afterward.

His outlook remained negative into his teens until he witnessed the exorcist Amasaki being turned away by his father. Learning of an exorcist gathering in Ishizuki Valley, he attended and met Takuma Yōsuke, whose compassionate aid inspired him. There, he also encountered the arrogant Seiji Matoba, sparking immediate friction. A test discerning a distant kimono's color revealed Natori's above-average, yet not exceptional, spiritual power, contrasting with Matoba's superior abilities. This motivated him to pursue exorcism, adopting glasses to sharpen his yōkai vision—a practice learned from Takuma.

Driven to prove his worth, he pursued a three-horned yōkai targeting exorcists. He refused Matoba's offer to collaborate, but his efforts failed; Matoba defeated the creature. This failure deepened his introspection about balancing strength and righteousness on his exorcist path.

As an adult, he maintains dual careers as a popular actor and leader of the revived Natori clan. Prioritizing human safety, his methods often involve forceful exorcisms fueled by ingrained resentment toward yōkai. This approach defined his initial interactions with Takashi Natsume, whom he recruited during a case involving the very yōkai from his childhood. When Natsume disrupted his exorcism ritual to protect her, the yōkai was freed and later became his shikigami, Hiiragi. This event forged their friendship despite differing philosophies on handling yōkai.

Natori commands three shikigami: Hiiragi, Sasago, and Urihime. His primary abilities involve manipulating paper dolls for attack, communication, or tracking. While his spiritual power is respectable, complex tasks require catalysts or assistance. A distinctive moving lizard mark on his body signifies his spiritual capability to those who perceive it; superstition suggests it avoids his left leg, foretelling future loss.

His bond with Natsume evolves into a protective, quasi-fraternal relationship. He conceals the Book of Friends' existence from Matoba to shield Natsume from exploitation, reflecting genuine concern. He frequently admonishes Natsume's recklessness in aiding yōkai yet supports him unconditionally, acknowledging their shared experience of isolation. This dynamic gradually softens his stance, leading him to adopt a middle ground between Natsume's pacifism and Matoba's ruthlessness. He remains willing to use force against threats but increasingly avoids it out of respect for Natsume's perspective.

His worldview is symbolized by his glasses, which sharpen his perception of yōkai but distort his view of the human world. Matoba observed this distortion reflects Natori's position between worlds: alienated from ordinary humans by his abilities yet not fully accepted by exorcists due to his power limitations. This duality fuels underlying bitterness but drives his commitment to protecting both realms on his own terms.