Fel is a legendary male magic beast of the Fenrir species and the first contracted familiar of the protagonist Tsuyoshi Mukouda. At over a thousand years old, specifically 1,014 years of age, Fel is an ancient being whose appearance is considered an extraordinary event, as he had not shown himself to humans for about three centuries prior to meeting his new master. He is a gigantic wolf with a beautiful coat of silver fur that possesses a luminous, glowing effect, while his legs are distinctly stained red, making his silhouette instantly recognizable and striking. His overwhelming presence is so awe-inspiring that simply being seen by humans is regarded as an almost miraculous occurrence.

Fel's personality is defined by his immense pride, dignity, and arrogance, as he generally looks down on humans as fundamentally inferior beings. He speaks to Mukouda using the term onushi, an informal way of saying you, and refers to his master as this guy when speaking to others, though he has once addressed him as master. He displays intense hostility toward anyone who attempts to command him besides Mukouda, going so far as to declare that he would destroy a country rather than obey such an order. Despite his lofty demeanor, he will not bare his fangs at children or the weak, and he is known to be surprisingly simple-minded at times. If someone steals his moment to shine in battle, he can become sulky and displeased, much like a child. His fellow familiar Dora-chan, a small dragon, has remarked that Fel is a bit of a worrywart, highlighting how much he frets over Mukouda's safety and well-being.

The motivation that initially drew Fel to Mukouda was the aroma of cooking. Tempted by the smell of a dish called red boar ginger pork, Fel voluntarily appeared and proposed becoming Mukouda's familiar in exchange for regular, delicious meals. Food remains a central driving force for him, as he is a voracious eater who especially loves meat and seafood while actively disliking vegetables and avoiding them when possible. His love of battle is equally significant, as Fel is a battle junkie who relishes fighting powerful foes, from chimeras to dragons. He agreed to hunt his own food for what he consumes, but because of his nature as a battle maniac, he hunts excessively, bringing down enormous numbers of powerful monsters, which often causes trouble for Mukouda, who must then arrange for the dismantling of the massive piles of monster corpses.

Within the story, Fel serves as Mukouda's primary protector and enforcer. He is fiercely protective of his master, attacking any enemy who threatens him with overwhelming force, sometimes to an overprotective degree. He forces Mukouda to practice combat skills, such as fighting goblins, to help him grow stronger, and he rewards his master with valuable monster parts like magic stones. Despite his terrifying power and reputation for being able to annihilate an entire nation by himself, Fel is a surprisingly simple creature driven by food and the thrill of combat.

His key relationships are deeply meaningful to his character development. With Mukouda, Fel acts as a powerful guardian who, despite his arrogant speech, reveals deep loyalty and concern through his actions. With Sui, a baby slime who becomes one of Mukouda's familiars, Fel shows a notably soft and indulgent side, allowing behavior he would never tolerate from others. Sui calls him Uncle Fel, a term that initially embarrasses him, but he ultimately permits the young slime alone to address him this way. His relationship with Dora-chan provides more humorous and humanizing moments, as the small dragon often comments on Fel's overprotective nature and worrywart tendencies.

Regarding his development, Fel is not a static creature of pure instinct. While he begins as an independent and fearsome magic beast, his contract with Mukouda and the subsequent addition of Sui and Dora-chan to their traveling party soften his edges and reveal his capacity for genuine affection and concern for others. His character arc involves learning to coexist and cooperate with other beings, including humans to some extent, as he accompanies Mukouda on his journeys and interacts with the adventurer's guild and various towns. He also demonstrates a willingness to teach, as seen when he allows Mukouda to feel the magic circulation in his body to assist him in learning spells.

In terms of abilities, Fel is effectively at the maximum level, with combat capabilities so high that he can instantly defeat S-rank monsters. According to the god Demiurgos, ancient dragons should be stronger than Fenrirs by species, but Fel's individual strength, combined with the blessing of the wind goddess Ninrir, allows him to fight on equal terms with ancient dragons, making him an exceptional, possibly the strongest Fenrir in history. He later also acquires the blessing of the war god Vahagn, granting him dual divine blessings that further enhance his already terrifying combat strength.

His magical repertoire is extensive and includes wind magic, fire magic, water magic, earth magic, ice magic, lightning magic, holy divine magic, barrier magic, and healing magic. He also possesses powerful combat and utility skills such as appraisal, claw slashing techniques, physical reinforcement, resistance to magical attacks, reduced magic power consumption, and overall combat enhancement. As a member of Ninrir's retinue, his divine protection from the wind goddess boosts his power and contributes to his ability to rival ancient dragons. He is highly knowledgeable due to his long life, can read human writing, understands human culture to a practical extent, and can navigate contracts, understand guild systems, and comment insightfully on the world around him. He can detect monsters with magic stones due to his high level and is immune to poison, disease, and physical irregularities thanks to his devotion to Ninrir. In his daily life, he acts like a noble lord traveling with his retinue, expecting good food and respect, and he detests baths, strongly disliking being washed or forced into bathing.