Sonoko Nogi hails from a prominent Taisha family, leading to a sheltered upbringing characterized by her dreamy, distracted nature. This seemingly detached demeanor concealed exceptional intellect and composure, revealed when her parents feigned collapse; she calmly reported their condition, timing, and summoned help. This defining trait shaped her future role.

Chosen alongside Washio Sumi and Minowa Gin in elementary school, she joined the original Hero team battling Vertexes. Her strategic mind and calmness under pressure earned her the leadership position. Initially friendless due to her eccentricity, she forged profound bonds with Sumi and Gin, especially after Gin's death in battle. She gifted Sumi her hair ribbon as a token of friendship shortly before their final mission.

During that mission, activating Mankai three times cost her right eye, left arm, and heart. After Sumi lost her memories from Mankai overuse, Sonoko activated Mankai seventeen more times, repelling twelve Vertexes alone. This left her with near-total paralysis, confining her to a hospital bed for years.

Following the events of "Washio Sumi is a Hero," she reappeared during a later Vertex invasion, summoning current Heroes to expose the truth about the Hero System and the Shinju's barrier. After recovering from Sange (Mankai's physical degradation), she enrolled at Sanshu Middle School and joined the Hero Club as an official member. Her personality retained its easygoing, dreamy quality, occasionally manifesting as imagining romantic scenarios between friends like Yuuna and Tougou.

Her combat abilities evolved. Initially wielding a multi-pronged spear, she later gained an enhanced version through her fairy, Kurama Tengu, capable of extreme extension. Her twenty-one fairies granted diverse powers: teleportation (Kurama Tengu), dream manipulation (Baku), and pillow-flipping (Makura Gaeshi). Taisha officials explicitly recognized her as the strongest Hero in recorded history.

Her Mankai form differed between media: the light novel depicted a giant spear with controllable blades, while the anime featured a warship resembling a Greek trireme with blade-like oars. This form generated energy shields and transformed into a bird firing lasers. Her repeated Mankai usage resulted in unparalleled destructive power, enabling elimination of multiple Vertexes simultaneously.

Relationships significantly shaped her. Her bond with Sumi/Tougou endured despite memory loss, rekindling when Tougou's memories returned. She initially felt unease around Yuuna post-recovery but quickly befriended her. Her original leadership contrasted with her supportive role in the Hero Club, interacting with members like Fu (whom she respected as fellow leaders) and Karin (who reminded her of Gin).

In "The Great Mankai Chapter," disillusionment with Taisha methods surfaced. She privately contemplated a coup to overhaul the organization and briefly wished for the world's destruction during crises. Yet, ties to the Hero Club, particularly Itsuki's influence, tempered these impulses. She ultimately chose reform over rebellion, assuming a Taisha leadership role to guide societal reconstruction.

Her ancestry links her to the earliest Heroes, particularly Nogi Wakaba, protagonist of the prequel "Nogi Wakaba is a Hero." This lineage explained her family's prominence and inherited heroic aptitude, though their personalities diverged. Historical parallels exist between her family name and the deified national hero General Nogi, though direct links remain unconfirmed.

Four years after the Shinkon Ceremony, she remained active coordinating recovery efforts alongside other Heroes, focusing on stabilizing society under the reformed Taisha. Her journey concluded with a commitment to ensuring humanity's coexistence with its divine protectors.