Akari Toki undertakes a mission with her twin sister Kagiri, tasked by their grandmother to retrieve a family heirloom dagger from Takeshi Chimatsuri. Takeshi's father legitimately won the dagger years prior in a duel against their own father. To achieve their goal, both sisters deliberately transfer into Takeshi's high school class, displaying minimal interest in academics while focusing solely on challenging him to regain the weapon.

Akari possesses an impulsive and harsh personality, often perceived as unfriendly, particularly toward males. She exhibits a severe aversion to physical contact with men, reacting with immediate, intense violence due to a deep-seated phobia. This hypersensitivity generates significant stress during confrontations. In contrast, she shares a close bond with Kagiri, frequently intervening to curb her sister's overtly provocative behaviors, such as disrobing to distract male classmates.

Trained since childhood in the Toki family's ninja arts, Akari demonstrates proficiency in stealth and combat. Her signature skill is molecular phasing, allowing her to pass through solid objects by synchronizing her atomic frequency with barriers or matter. This technique renders her temporarily intangible, enabling evasion of attacks and undetectable infiltration. She can extend this ability to objects or people through physical contact. Her mastery includes advanced applications like dispersing her molecules to erase all sensory presence, including spiritual energy, effectively becoming invisible.

Akari and Kagiri employ diverse tactics against Takeshi, exploiting his "female allergy" (a vulnerability to nudity or suggestive situations), using invisibility elixirs, creating elaborate disguises, kidnapping allies, and piloting a clockwork mech. Despite their ingenuity, Takeshi often outmaneuvers them, partly because Akari's phobia undermines her focus during close engagements.