Fū is a thaumaturge mage and a member of the Argentum Corps, the military unit led by Staria Reze that serves as humanity's main offensive force against the dragons. Before the events of the story, Fū was involved in the distribution of new types of drugs across the region of Reze. His criminal activities brought him to the attention of Staria Reze, who forcibly conscripted him into the Argentum Corps as an alternative to punishment. He operates under a false name, with his real identity being unknown to most of his comrades.

Fū presents a harsh and inflexible exterior, often speaking in a sarcastic and crude manner. He has a strong perfectionist streak and takes immense professional pride in his magical creations, particularly his magic circles. This pride makes him sensitive to any perceived improvements or alterations made to his work by others, sometimes to the point of tears of disappointment. Despite his gruff and difficult temperament, this demeanor masks a hidden sentimental side, most notably a secret, protective affection for Majorca Abbott, whom he treats with constant rudeness and verbal abuse, frequently calling her ugly. This behavior serves to conceal his true relationship with her.

Within the Argentum Corps, Fū serves as the head of a special unit dedicated to magical combat. His primary role is the creation of complex magical circles, with a specific focus on teleportation magic, which is essential for evacuating civilians and troop movement during large-scale operations. He is an exceptionally talented mage, specializing in high-level combat magic including killing spells and absorption magic.

The most significant relationship in Fū's life is with Majorca Abbott. While he constantly berates and insults her, the truth is that he is her older brother, a secret he works to maintain despite her being fully aware of the familial bond. He shares a complicated dynamic with Isaac Stern, accepting money from him to maintain certain secrets and to protect Ragna and his team. He also has a connection to Crimson, who forcibly seeks to improve his magic circles, which challenges Fū's professional honor. Staria Reze is the one who forced him into service, acting as both his savior from punishment and his commanding officer. Fū also has a peculiar physical trait, as his right arm hides mysterious characteristics of a dragon. His typical speaking style includes a marked western dialect.

Fū's responsibilities in the story center on creating the necessary magical infrastructure for the corps' battles. He is responsible for developing large-scale teleportation magic circles, which were originally ordered by Majorca Abbott for use in a planned coup. He is also instrumental in hiding Ragna and his companions when Isaac Stern attempts to pressure him. During a battle against the dragon Olto Zora, Fū's magical abilities are pushed to their limit. To fight effectively, he injects himself with his own drugs and directly absorbs magic from the enemy, an act that results in the loss of his lower limbs. In a final effort, with support from Isaac Stern and Christopher Algren, he unleashes his most powerful killing magic, succumbing to exhaustion and his injuries afterward.

In terms of abilities, Fū is a highly skilled mage whose power lies not in direct combat but in the creation and utilization of magic circles. His most notable skill is the creation of powerful teleportation circles, which are strategically invaluable. He also demonstrates mastery over killing magic and absorption magic in combat situations. His magical prowess is such that he can even absorb magic directly from a dragon, though doing so carries severe physical consequences. His unique physical trait, the draconic characteristic in his right arm, may also be linked to his magical abilities.