Dokuro Mitsukai is an angel assassin dispatched from the future by the order Lulutie (sometimes called Rurutie). Her mission targets junior high school student Sakura Kusakabe, destined to create technology granting immortality while halting female physical aging at twelve. Defying divine orders, she spares Sakura, believing his future path can be changed without killing him. This act of rebellion pits her against heaven and triggers the arrival of other assassins, like Sabato.

She manifests as a perpetually twelve-year-old girl possessing superhuman strength and endurance, often accidentally harming Sakura during everyday contact by underestimating her power. Her primary weapon is the magical spiked club Excalibolg, used to inflict fatal wounds. Dokuro also wields a distinctive chant, "Pipiru piru piru pipiru pi," enabling her to resurrect the dead, a power frequently employed to revive Sakura. Additional magical abilities include transforming humans into animals or erasing them from existence.

Her personality is impulsive and volatile, marked by sudden violent outbursts. Minor provocations—like accidental peeping, misunderstandings, or her own frustration—often trigger these episodes, resulting in Sakura's brutal death via bludgeoning, dismemberment, or decapitation. Despite this aggression, she demonstrates protective instincts, living with Sakura to guard him against threats, particularly Sabato. She expresses affection through teasing and sexual innuendo, gradually becoming more comfortable with Sakura viewing her nude. Her speech consistently ends every sentence with "dayo."

Key relationships define her behavior. She harbors romantic feelings for Sakura, leading to jealousy-fueled violence when his attention shifts to others, such as classmate Shizuki. Her dynamic with fellow assassin Sabato alternates between adversarial conflict and casual friendship, collaborating when not directly opposing each other over Sakura. She shares a sisterly bond with Zakuro Mitsukai, though Zakuro occasionally suggests Dokuro should eliminate Sakura.

Beyond assassination, Dokuro founded a school club dedicated to observing wood glue dry. She secured faculty approval through unspecified coercive methods and forcibly recruited Sakura as a member, aiming to advance the club to national competitive levels.

Her background reveals her as a dissident within the angelic hierarchy, defying orders by protecting Sakura. This rebellion stems from her conviction that Sakura's future is alterable through persistent distraction rather than execution. Her personality and methods show no significant evolution across official media.