Diavel numbered among the 10,000 players imprisoned within the deadly virtual reality game Sword Art Online, publicly known as one of its few beta testers. Roughly two months after the game began, he rose to lead the raid party confronting the first floor boss, Illfang the Kobold Lord. He possessed blue hair with long bangs and blue eyes. His attire consisted of bronze armor protecting his chest, shoulders, arms, and shins, worn over visible blue clothing. A large longsword hung at his left waist, and he carried a kite shield on his back. Diavel's personality displayed a dual nature. Publicly, he acted as a strong, natural leader, inspiring players with determined speeches and commanding the raid with effective tactics that initially kept casualties low. Privately, he harbored ambitions for personal prominence and saw Kirito as his rival. To undermine Kirito, Diavel attempted to buy Kirito's «Anneal Blade» using Kibaou as an intermediary, hoping to reduce Kirito's attack power. When this failed, he strategically assigned Kirito to fight Illfang's minions, the «Ruin Kobold Sentinels», to prevent Kirito from landing the Last Attack bonus on the boss, which Diavel intended to claim for himself. During the boss encounter, Diavel's leadership guided the raid party with near-flawless execution as they depleted Illfang's health. When the boss entered its critical phase, Diavel charged forward, expecting Illfang to switch to a Talwar as in the beta. Instead, Illfang drew a Nodachi with a completely altered attack pattern. This unexpected deviation caught Diavel off-guard, resulting in a deadly combo strike that eliminated his hit points. With his final moments, Diavel entrusted Kirito with defeating Illfang and saving the remaining players. Diavel's death triggered far-reaching consequences. It directly fueled the raid party's hostility toward beta testers, prompting Kirito to adopt the stigmatized label "beater" (beta cheater) to diffuse tensions. This event also catalyzed systemic distrust among frontline players, fracturing raid group dynamics. Narrative portrayals of Diavel vary between media. The original light novels and Progressive adaptations emphasize his manipulative actions against Kirito, while the anime adaptation omits these nuances, presenting him as a more selfless figure despite retaining his pursuit of the Last Attack. His name translates to "Devil" in an Italian dialect (Romansch), and he self-identified as a "knight" despite Sword Art Online lacking formal character classes.