Fieri Yunis is the father of Yuna Yunis and Millie Yunis, and he is also a member of Millie's adventuring party. He hails from a prestigious martial arts lineage and is a formidable fighter who employs his own Yunis-style Fist Combat technique in battle. His skills were formally recognized when he once held the esteemed position of being one of the Four Knights of the Farom Kingdom.

Despite his combat prowess and noble origins, Fieri has significant character flaws that have shaped his life. He possesses an obsessive fondness for women with large breasts, a fixation that proved to be his undoing as a knight. His constant harassment of the female knights in the order led to him being sued, stripped of his title, and ultimately exiled from the royal capital. This banishment reflects a key aspect of his personality: while a skilled warrior, his personal vices and lack of self-control have real consequences.

In the story, Fieri initially views the protagonist, Touka Scott, with disdain, considering him nothing more than a pervert with a thigh fetish. This negative perception is a source of conflict, as it leads him to oppose his daughter Yuna's decision to go on adventures, presumably due to his low opinion of her companion. However, his stance is not static. Following the fierce battles in the region of Elbania, Fieri is forced to re-evaluate Touka. Witnessing Touka's actions and growth during these events leads him to change his mind. He comes to respect Touka and ultimately grants his permission for Touka to remain by Yuna's side as a supporter in her journey. This development shows that beneath his crude exterior, Fieri is capable of changing his judgment and prioritizing his daughter's well-being over his personal biases.