Vanir originates as a Duke of Hell within an oligarchy ruling the infernal realm and waging primordial wars against gods. This entity operates by possessing humanoid forms through masks while concealing its true body in Hell. After contracting with the Devil King, Vanir served as a general maintaining the castle's barrier but predominantly taunted minions for their negative emotions via shapeshifting pranks. A pivotal encounter involved adventurer Wiz, whom Vanir repeatedly defeated until she deployed a flawed barrier item. When Wiz later offered her soul during a fierce battle, Vanir taught her the forbidden ritual to become a lich. Subsequently resigning as general, Vanir occupied Keele's Dungeon to construct a perfect dungeon for achieving a personal dream: luring adventurers to defeat it, only for them to discover an empty treasure chest, allowing Vanir to savor their profound disappointment before their demise. Kazuma's party interrupted this scheme, leading to a confrontation where Vanir possessed Darkness but was defeated by Megumin's Explosion magic, costing one life. Reborn with a mask marked "II," Vanir relocated to Axel, working at Wiz's Magic Shop under a contract to fund the dream dungeon through business success. In Axel, Vanir actively enforces trash disposal rules, chases crows—earning the moniker "Crow Slayer"—and establishes an Adventurer's Guild consultation service. Business dealings with Kazuma involve marketing otherworldly inventions like the kotatsu while sharing profits. Powers encompass divination for mind-reading and foresight—weakened against potent targets or divine interference—alongside conjuring explosive dolls, firing "Vanir-Style Murder Ray" eye beams, cursing targets to alter physiology, possessing others via masks, summoning demons, and resurrecting through spare masks. Relationships include a close partnership with Wiz, adversarial clashes with the goddess Aqua as natural enemies, mutually beneficial transactions with Kazuma, and protective oversight of territory-bound demons like succubi. In a parallel world, Vanir teaches Class 1 and occasionally Class 2. The character dons a black-and-white "II" numeral mask and a formal blue suit with white gloves. Personality traits involve relishing chaos and harvesting negative emotions like shame or disappointment through public teasing, pranks, and secret-exposing—all while adhering to self-imposed rules against harming humans. Vanir exhibits theatricality, dramatic speech, pride in demonic status, and self-references as "moi." The ultimate ambition remains constructing a dungeon to experience a dramatically satisfying demise fueled by exquisite disappointment.