Tōko Aozaki, the older sister of Aoko Aozaki, is a highly skilled magus trained from childhood by her grandfather at his mountain workshop in Misaki Town. This early tutelage set her firmly on the path of sorcery, distinct from her sister who lived with their parents. Her first love was Eiri Fumizuka, an apprentice of the Aozaki clan, though those romantic feelings have since faded. At fourteen, she studied in London for two years before returning to Japan and enrolling at Reien Girl's Academy. There, she shone as an honor student with a bright personality, earning recognition as one of the dormitory's "three shining stars." Her life fractured when her grandfather unexpectedly designated the informally trained Aoko as the successor to the Fifth Magic. Fleeing to England, Touko joined the Mage's Association, cementing her deep-seated rivalry and hostility towards her sister.

At London's Clock Tower academy, Touko pursued the less popular field of rune studies, specializing in stabilizing runic characters. Simultaneously, she advanced her expertise in puppet-making, driven by the goal of recreating the original human body. Her research into reaching the Root (Akasha) was ultimately abandoned upon concluding modern humans could no longer achieve it genetically. During her studies under Inorai Valualeta Atroholm, she connected with peers Souren Araya and Cornelius Alba. She rivaled Araya over their shared objective of reaching the Root, while Alba sought her acknowledgment. Achieving the Clock Tower's highest distinction, the rank of Grand, by age twenty, her triumph was marred. Denied her preferred epithet "Blue" (reflecting her surname "Aozaki"), she was instead branded "Scarred Red" – a slight further fueling her resentment towards Aoko, the inheritor of "Blue."

Deemed too problematic, Touko left the Mage's Association and adopted a nomadic existence. She famously purchased the werewolf Lugh Beowulf with twenty years' worth of her hair, renaming him "Beowulf." Lacking binding magecraft to control him, he accompanied her across Europe, drawn by her "good scent" and the promise of battling powerful Mysteries. Their exploits included encounters with a train collecting Mystic Eyes, an ancient giant octopus, the Bermuda Triangle's otherworldly portal, and an Elder Dead Apostle Ancestor. In a separate incident, she killed the demon magus Francesca thirteen times in retaliation for being called "Scarred Red," destroying her workshop and stealing magical items each time. Francesca managed to kill her once, but Touko activated a new puppet body and continued her rampage until Aoko intervened.

Tōko operates as a puppet maker and architect, running the detective agency Garan no Dou, which handles supernatural cases. She employs Mikiya Kokutō and later Shiki Ryōgi. Her appearance is that of a woman in her late twenties, maintained through her puppet bodies which "fix" her physical form. She habitually wears an orange accessory despite disliking the color association and is a heavy smoker of the rare brand Dragon Smoke. Her glasses function as Mystic Eyes Killers, and her personality shifts dramatically depending on whether she wears them: with glasses, she appears calm, objective, and ruthless; without them, she becomes subjective, emotional, and cruel. This duality renders her true personality ambiguous, even to herself, though she identifies as a romanticist at her core. She values practical skills over certifications, holding qualifications in Medical Treatment, Construction, Business, and Information Gathering.

Her character evolves from an obsession with reaching the Root and avenging Aoko towards a more grounded existence. Initially, she withheld salaries from employees like Shiki due to impulsive spending on magical artifacts from "Dark Amazon," often leaving herself financially strained. Gradually, she prioritizes daily life and relationships, notably remaining longer than usual with Mikiya, Shiki, and Azaka Kokutō. Her dynamic with Aoko shifts from outright hostility to a contentious but persistent connection, exemplified by her buying items under Aoko's name as retaliation for stolen sunglasses—even at the risk of exposing her location. In later years, she departs from Garan no Dou, leaving Mitsuru Kamekura to manage the agency under Shiki Ryōgi's leadership. Though no longer driven by grand ambitions, she continues her work as a magus, leveraging her extensive knowledge across all branches of magecraft and mentoring apprentices like Azaka.