Claire Fugo belongs to the Fugo family, historically linked to magic. She performs tarot divinations and demonstrates notable talent as a gymnast. During childhood, Claire frequently played with Shingetsu Ernesta Fukami, who temporarily lived with the Fugo family, and with her sister Anna. After Shingetsu left, Claire didn't see her again until a chance street encounter years later. Claire enthusiastically embraced Shingetsu and shared news of an upcoming gymnastics competition, but Shingetsu apologized and walked away, leaving the reunion unresolved. Claire later informed Anna she had located Shingetsu's school, visibly frustrating Anna.

Months afterward, Claire conducted a tarot reading in the Fugo residence, unexpectedly drawing the 'Nothingness' card. Consultation with Suishou Hakamada revealed this was a warning from the house of impending danger. This warning proved accurate when Claire's mother was attacked by thieves targeting the Fugo family's magic stone, necessitating Claire's hospital visit.

On a full moon night, Claire encountered Anna, now possessing the stolen stone. Claire tearfully questioned if Anna felt loved by Magiaconatus, referencing her mother's belief that only those loved by it could win GRANBELM. She expressed her deep desire for herself, Anna, and Shingetsu to reunite and play like they did as children. Anna countered that her only goal was to hurt Shingetsu, explaining her spirit had shattered long ago, and then apologized before vanishing.

Following Anna's defeat in GRANBELM and her erasure from existence by Magiaconatus, Shingetsu, Mangetsu, and Kuon traveled to the Fugo residence to confirm Anna's fate. Before they arrived, Claire emerged cheerfully accompanied by Rosa, whom she affectionately called 'big sister'. Magiaconatus had substituted Rosa into the family history in Anna's place. Later, Claire was observed walking to school with Rosa, playfully balancing on a thin rail to demonstrate her gymnastic ability. She briefly sensed Shingetsu's presence but turned a moment too late.

Claire maintained a persistent affection for Shingetsu throughout the years, contrasting with Anna's growing resentment, fueling her hope for Shingetsu's return to the family. The erasure of Anna's existence caused Claire to completely forget Anna had ever existed, a consequence of Anna's actions to distance Claire from Shingetsu. Historically, Claire often sought physical closeness with Shingetsu. In the reconfigured family dynamic after the magical alteration of reality, Rosa occupied the role of the Fugo family's elder daughter, with Claire embracing her as an older sister.