Nana Hiiragi arrives as a cheerful transfer student exhibiting telepathic abilities, marked by teal eyes and bubblegum pink hair with white tips, typically styled in pigtails secured by daisy-adorned hair ties. She dons a bright red-pink and white school uniform during her island assignment. Post-timeskip, her hair lengthens while maintaining pigtails, and she switches to a navy blue Watchman uniform.

Her fabricated persona mimics an airheaded, socially inept extrovert who vocalizes thoughts indiscriminately. Concealed beneath this facade is a calculating, observant, and ruthless government assassin operative. This true personality employs exceptional deductive reasoning and strategic planning to manipulate events, often camouflaging her maneuvers with performative clumsiness.

Her traumatic past includes government-employed parents murdered by agent Tsuruoka after they questioned the ethical treatment of the Talented; he framed their deaths as a Talented burglar’s work. Tsuruoka then took custody of Nana, subjecting her to psychological manipulation and abusive conditioning to instill self-hatred and belief in the Talented as humanity’s enemies. This indoctrination molded her into a child soldier tasked with eliminating superpowered individuals.

Deployed to an isolated island academy posing as a student, her mission targets Talented classmates deemed existential threats by the government. Feigning telepathy, she exploits acute observational skills to deduce talents and weaknesses, engineering scenarios to assassinate targets undetected. Early actions include pushing class leader Nanao Nakajima off a cliff after gaining his trust and orchestrating the drowning of time-traveler Yohei Shibusawa by exploiting his exhaustion and inability to swim.

Interactions with classmates—particularly Michiru Inukai—trigger her psychological evolution. Michiru’s unconditional kindness and self-sacrifice, culminating in her death while healing Nana, fracture Nana’s resolve to kill. This fracture becomes catastrophic when Tsuruoka reveals his role in her parents’ murders, exposing government deception and shattering her foundational motivations. The revelation drives her to a suicide attempt, halted only by her resolve to atone.

Post-timeskip, Nana shifts toward redemption, allying with former targets like Kyouya Onodera to expose government corruption and protect Talented students. Expressing profound remorse, she prioritizes saving lives—including Nanao, who survived her assassination and now opposes both factions. Her strategy pivots from infiltration and murder to hostage negotiations, intelligence gathering, and disrupting government operations, all while battling persistent self-loathing.

Key relationships define her arc: her adversarial dynamic with Kyouya evolves into mutual respect through shared deductive prowess; her bond with Michiru awakens latent empathy; her vendetta against Tsuruoka fuels her commitment to dismantling the system that weaponized her. Despite evolution, she retains traits like animal affection—sparing Kyouya’s cat during an assassination—and strategic obsession, creating complex solo board games stemming from childhood social isolation.