Vearn stands as the primary antagonist throughout the Dragon Quest: The Adventure of Dai narrative. Originating as a darkling, he ascended to become the God of the Underworld following his kind's confinement there. Millennia of existence fueled his deep resentment toward humanity for their access to sunlight, a blessing he coveted for the underworld. This drove his ultimate goal: annihilating the human world to redirect the sun's light to his realm. For thousands of years, he meticulously plotted this destruction, amassing resources and armies while implementing protective measures for himself. He maintained a rivalry with Velzar, the Abyss Dragon King, which settled into a truce where each pursued separate plans to overthrow the gods. To achieve immortality, Vearn divided his body: one half preserved eternally young through the Secret Spell of Frozen Time, the other aging but accumulating magical power. He entrusted his younger body to Myst, who merged with it to become Mystvearn. Vearn later established the Dark Army, resurrecting the defeated Dark Lord Hadlar as its Supreme Commander and recruiting powerful allies like Baran, Dai's father, by exploiting his hatred toward humanity. The Sovereign Rock Castle served as his mobile headquarters.

Physically, Vearn initially presents as a tall, elderly figure with pointed ears, black horns, a long beard, white hair, and a distinctive third eye—the Sovereign Eye—on his forehead. He wears ornate white robes, a purple chestplate, black shoulder pads, and a crown. This frail appearance masks his true power, often leading to underestimation. After merging with his preserved youthful body, he transforms into a muscular, silver-haired demon nearly three times taller than a child, with straightened horns and golden eyes, now clad in simpler white pants and a jacket. His ultimate form, Sovereign Supreme, results from plucking his third eye to unleash its stored power irreversibly. This monstrous, crustacean-like entity stands over thirty meters tall, encased in rocky armor with a giant eye on its chest, significantly enhancing his physical strength and durability at the cost of his original magical versatility.

Vearn's personality blends calculated patience with absolute social Darwinism. He views strength as the only true law of nature, considering humanity weak and unworthy of the sun's blessings. Despite this contempt, he pragmatically acknowledges human potential for growth, particularly after witnessing Avan's earlier defeat of Hadlar. He treats subordinates like Hadlar, Mystvearn, and Killvearn with a degree of fairness, offering multiple opportunities to redeem failures, yet ultimately sees them as expendable tools. This is starkly demonstrated when he implants a Black Core bomb inside Hadlar without his knowledge, planning to detonate it to eliminate enemies continentally—an act that eventually triggers Hadlar's betrayal due to its perceived cowardice. Vearn relishes psychological manipulation, delivering speeches designed to shatter opponents' ideals of hope and justice, though he respects resilience and passion in both allies and enemies. His strategic mind is reflected in his love for chess, viewing warfare through its principles of concealed intentions and decisive final moves. However, his stated adherence to "no cheating" contrasts with his own underhanded tactics. When cornered or defied, his composure fractures into rage-fueled desperation, especially after critical setbacks like the revelation of Gome's true nature as a wish-granting entity or the collective human resistance countering his genocidal plans.

Vearn's magical and combat abilities are unparalleled. Millennia of cultivation allow him to cast spells with unprecedented power and efficiency, such as amplifying basic Frizz spells beyond others' ultimate variants like Kafrizz, or spamming high-level Boom spells continuously. His signature techniques include Kaiser Phoenix, a fiery bird manifestation of Kafrizz, and Aura Shot, a dark energy burst capable of shattering structures instantly. He wields the Staff of Edacity, which converts mana into physical force, enabling him to shatter orichalcum and block powerful attacks, though it drains mana over time. His physical prowess is formidable even in his elderly form, but peaks after merging with his youthful body, granting him techniques like Phoenix Wing (parrying and reflecting attacks bare-handed) and Calamitous End (devastating hand strikes). His Tenchi Mato stance combines defensive and offensive techniques to counter multiple simultaneous assaults but leaves him momentarily vulnerable afterward. The Sovereign Eye provides unique abilities: imprisoning weaker foes in jewels, inducing monster evolution (e.g., transforming a Drumbler into the gravity-controlling Goroa), and enabling his final transformation. Vearn also possesses three hearts, regenerative capabilities allowing instant recovery from lost limbs, and an automatic Fullheal akin to the Prezing spell when critically damaged.

Throughout the story, Vearn evolves from a hidden manipulator to an active combatant. Initially operating behind a veil, he orchestrates the Dark Army's campaigns through Hadlar while monitoring key events like Baran's battle with Dai. He demotes Hadlar after commanders fall but reinstates him upon his evolution into a Superior Being. His direct involvement escalates after Hadlar's betrayal: he confronts the heroes personally, employing psychological and physical domination. Critical moments include his shock upon witnessing Dai's dual Dragon Crests—marking him as a genuine threat—and his failed attempt to detonate Hadlar's Black Core, which Baran contains sacrificially. Vearn's scheme to lure heroes via Hyunckel and Crocodine's fake execution culminates in the assault on his flying palace. After Dai defeats Hadlar, Vearn tries to kill them both with traps, leading to the final battle where he assumes his Sovereign Supreme form. This battle concludes with his defeat, and his remains drift toward the sun—an ironic fate given his obsession with it.