Nanao Nakajima emerges from a wealthy family dominated by high expectations, particularly the relentless pressure from his father demanding leadership in all situations. Constant comparisons to his two older brothers forged deep-seated insecurities and an inferiority complex, cementing his status as the family's "least talented" member. His childhood featured small deceptions—like falsely claiming to share lunch with a hungry classmate—prioritizing paternal approval over authentic kindness.

Enrolling at the isolated academy for the Talented, Nanao deliberately concealed his true ability to nullify other Talents through physical contact, presenting himself as powerless to evade attention. This facade invited persistent bullying from classmates like Moguo Iijima, who mocked him as "talentless" and "Self-Proclaimed Leader"—a taunt referencing his failed declaration as class leader upon arrival. His shy, anxious exterior masked a volatile temper, especially regarding family inquiries.

His trajectory shifted with the arrival of Nana Hiiragi, who falsely claimed telepathy and befriended him. She nominated him for class representative, citing his diligence and kindness, though he declined due to crippling self-doubt. After covertly using his nullification to save classmates during a confrontation, he briefly gained confidence and acceptance. This trust shattered when Nana betrayed him, luring him to a cliff and pushing him to his apparent death after provoking him about his familial failures.

Miraculously surviving the fall, Nanao was captured by government operative Tsuruoka and subjected to extensive brainwashing. This process obliterated his former kindness, forging a ruthless persona marked by bloodlust and manipulative cunning mirroring his mentor. He embraced the identity of "truly an enemy of humanity" and manifested a mutated nullification ability. This evolved power could neutralize biological functions like heartbeat or breathing, suppress moral inhibitions to create temporary killing machines, or induce sensory deprivation rendering him invisible.

Reappearing after a three-year timeskip as Tsuruoka's second-in-command and Special Director of a Managed Camp designed to segregate Talented individuals, Nanao now wore military uniform with longer hair tied in a low ponytail. He enforced brutal policies, leveraging his evolved powers to control or eliminate targets. He oversaw the extraction of his own brain cells to create drugs temporarily suppressing Talents, advancing the government's agenda.

His final confrontation culminated in a battle with Nana Hiiragi. After killing her, he committed suicide, declaring his actions unforgivable. This outcome was subsequently reversed via a time-loop ability employed by another Talented individual, undoing both deaths.