Gustav

The chief medical officer in charge of Xenobia's medical examinations. His true identity is a high-ranking demon (Archdemon) under the original Violet (Viore). He was secretly working to make Xenobia a vessel for Viore, but his true identity was exposed due to the investigations and efforts of Rimuru and his team. He fought to erase the evidence and for the manifestation of Viore, but was stopped by Luminous and was deemed useless by Viore, who then disposed of him.