When Lina Inverse first encounters Vileus, he and fellow beastman Rudia are acting as bodyguards for Krotz. When Krotz sees the body of Balgumon, recently killed by Xelloss, he orders Vileus and Rudia to awaken Grouj. The two beastmen refuse, as Grouj has become violent and unpredictable since donning a set of Zanaffar Armor. Krotz then orders the beastmen to fight Lina and her party while he awakens Grouj himself.
However, instead of fighting Lina, Vileus and Rudia ask her to help them. They are afraid of Grouj and fear for Krotz's safety. Rudia offers to lead Lina to him if she promises not to harm Krotz while dealing with Grouj. Before they can reach Grouj, however, Krotz succeeds in awakening him. Grouj's armor consumes him entirely and becomes the second Demon Beast Zanaffar.
Vileus and Rudia join the Slayers in fighting Zanaffar, but both quickly perish. Rudia, the more reckless of the two, is killed first. Vileus is more cautious; however, when Zanaffar speaks and reveals that it has consumed Krotz, he loses his composure and charges the Demon Beast. Zanaffar effortlessly cleaves him in half using beams of light, similar to laser breath, projected from the tips of its tentacles.