Akari Tokitō is a first-year student from Japan's Nishichou High School. Her life was defined by loneliness and isolation, worsening after the disappearance of her best friend, Hakua Shirakami. Akari insisted on keeping Hakua's seat empty, leading classmates to bully her by placing flowers on the vacant desk as a taunt.

Forcibly summoned to another world by the aristocratic Noblesse caste to be used against the Faust religious organization, Akari gained the Pure Concept of Time. This power, improperly fused with her soul, grants near-invulnerability through temporal manipulation. Its manifestations include Regression (reverting entities or the world to prior states), Suspension (halting time for targets), Weathering (accelerating decay), and Acceleration (increasing relative movement speed). Overusing these abilities risks memory degradation and spatial-temporal disruptions, potentially transforming her into a catastrophic Human Error.

Akari displays a carefree, naive demeanor, embracing the new world as an escape from her past loneliness. She forms an immediate, intense attachment to Menou, an executioner tasked with eliminating her, believing their meeting was fate. This devotion leads her to volunteer to strip in Menou's place during a hijacking and express unwavering trust, granting Menou painless access to her powers. Akari frequently declares her love for Menou and insists she will only accept death at Menou's hands.

Her existence is defined by repeated temporal resets. Witnessing Menou and Momo die from Flare's Sword of Salt in the original timeline triggered her first World Regression. Subsequent timelines involved varied strategies: escaping the Noblesse castle alone to protect Menou, or confronting Flare directly after learning of Menou's death. Each regression eroded her memories of Japan and Hakua, pushing her closer to becoming a Human Error. To mitigate this, she implemented memory locks, erasing knowledge of past loops while preserving her affection for Menou. Her singular goal drives these resets: finding a timeline where Menou survives, even if it requires her own death.

In the current timeline, she journeys with Menou under the pretense of seeking a way home while secretly manipulating events toward her objective. During crises, she temporarily regains past memories to deploy her powers strategically before self-administering Regression: Memories, Soul and Spirit to revert to ignorance. This cyclical existence underscores her tragic resolve to sacrifice her identity repeatedly for Menou's survival.