Fefnir is one of the Four Guardians of Neo Arcadia, a battle-hardened warrior who thrives in combat. He has a deep love for battle, and the more intense the fight, the more he enjoys it. However, Fefnir is not a mindless fighter—he has a sense of honor that drives him to seek clean, one-on-one duels, particularly with Zero, whom he sees as both a rival and a worthy adversary. Fefnir is proud of his position in Neo Arcadia and views the world under Master X’s rule as a peaceful utopia, despite the violent methods he employs to maintain it.

While Fefnir is unquestionably loyal to X and his vision of Neo Arcadia, his loyalty is tempered with a sense of personal pride, which sometimes leads to arrogance. He’s willing to do what’s necessary for Neo Arcadia’s sake, but he’s also not afraid to voice his opinions—especially when he believes his skills or his position should be respected. Fefnir has a rivalry with both Zero and Harpuia, as he both envies Zero’s connection to X and mocks Harpuia’s failures in battle. Despite this, he values honor above all else and is willing to put aside his pride when it comes to fulfilling his duty.