Akio Fudo is a magic user who serves as the Third Seat of the Grimoire Security, an organization that monitors magical threats, and is a member of the Trinity Seven with the Gula Archive representing the sin of gluttony. She was born and raised in a town beneath the Sky Library, where she and her mother lived as Spriggans, hereditary guardians of the legendary weapons stored there. After her father died of illness, the entity known as Abyss Trinity destroyed her hometown out of boredom. Akio’s mother used her last magic to shield her daughter, sacrificing herself and leaving Akio as the sole survivor. This tragedy shaped her research Thema, Fides, meaning faith.

Despite her painful past, Akio is generally cheerful, easygoing, and calm even in dangerous situations. She enjoys banter and teasing her close friends, and she has a notable love for combat, earning her a reputation as a battle maniac. Beneath her lighthearted exterior, she is intensely loyal and protective. She can be pragmatic and even ruthless when considering threats, once suggesting that a potential catastrophe be prevented by extreme measures, but she quickly dismisses the idea due to her growing fondness for the person in question. Akio also shows unexpected innocence, becoming flustered and embarrassed when her clothes are accidentally removed, despite not being inherently shy. She is the partner and closest friend of Mira Yamana, having reached out to a reclusive Mira in the past and helped her accept her power. Akio also shares a friendly rivalry with Levi Kazama, and she is being trained by Murakumo Amane to become an Arbitrator, sharing a sisterly bond over their love of battle.

Akio specializes in Mantra Enchantment, a form of magic that involves inscribing mantra characters onto her body to enhance her physical abilities, particularly her powerful kicks. The effectiveness of her magic depends on her emotional resolve, as weak determination can cause self-inflicted damage. She also possesses healing capabilities and can transfer her knowledge to other magic users. As a battle magus, she maintains zero magic consumption until she attacks or defends. Uniquely among the Trinity Seven, she lacks a personal grimoire. Excessive magic use triggers her Hungry Mode, also known as empty stomach mode, which transforms her into a younger-looking girl dressed in a nun’s habit. This form reduces her overall magical capacity but concentrates her offensive power. Outside of combat, Akio works part-time as a chef at a restaurant where Mira works as a waitress.