Gunbard is a former knight who found an infant girl, Yucie, in a basket near a battlefield after defeating a mage. He adopted her as his daughter, retiring from knighthood while retaining his noble status. In his youth, he served as Queen Ercell's personal guard and developed a romantic relationship with her, despite his commoner status versus her royalty. To become eligible to marry Ercell, he embarked on a quest to assemble the legendary Eternal Tiara. This required collecting gemstones representing the five worlds—Human, Heaven, Demon, Fairy, and Spirit—by overcoming guardians, completing trials, and forging the tiara at a mystical location.

Returning with the completed tiara, he learned Ercell had married another man due to her father's failing health and final wish. Heartbroken, he left the palace, abandoning the armor and sword Ercell had gifted him, and resumed military campaigns. After finding Yucie, he dedicated himself to raising her, building a home and employing the exiled demon Cube as a servant and steward for her.

As Yucie's father, Gunbard exhibits deep affection but is excessively overprotective and indulgent, overwhelming her with large birthday feasts and spoiling her during school breaks. His demeanor is generally cheerful and energetic, though he struggles socially outside his family and becomes serious during combat or crises. He possesses practical skills like cooking and alchemy, creating energy drinks to alleviate Yucie's stress.

He supports Yucie's enrollment as a Platinum Princess candidate at Queen Ercell's academy, viewing it as an opportunity for her growth. When Prince Arc—later revealed as Yucie's childhood savior—seeks him to confirm suspicions about his paternity, Gunbard denies being Arc's father. He affirms the late king's role and draws a parallel to his own adoptive relationship with Yucie. During the Diabolos crisis, he delays Arc's curse using his abilities and opens a portal to the location of the final tiara component, leveraging knowledge from his original quest.

Following Yucie's ascension as Platinum Princess and her grief over forgotten memories, Gunbard feels responsible for her pain due to his role in reassembling the tiara. He collaborates with other realm rulers to open a gateway to the Magic World, enabling Yucie and Arc to restore what was lost. He never discloses his creation of the Eternal Tiara to Yucie.