Vater leads the White Night guild with significant authority. He first met Kufa Vampir ten years before the main events during a mission to eliminate the Testament-level Lancanthrope, Naqua. Kufa, then a child, had just transformed the mortally wounded Rosetti Pricket into a vampire to save her. Vater arrived with soldiers, confronting Kufa about Rosetti's irreversible blood craving. Kufa negotiated a deal: he offered to seal Rosetti's memories and swear lifelong loyalty to Vater and the guild in exchange for her life being spared. This pact led to Kufa's intense training and eventual role as a key guild assassin.

Years later, Vater assigned Kufa a critical mission involving Melida Angel. He instructed Kufa to tutor Melida while secretly assessing her ability to manifest mana, proof of noble lineage. If she failed, Kufa was ordered to assassinate her, driven by suspicions about her parentage. After Kufa defied orders by giving Melida his own mana instead of killing her, Vater doubted Kufa's reports and initiated his own investigation.

In Volume 10, Vater escalated by ordering Kufa to assassinate both Melida and her cousin Elise Angel as a final loyalty test. Kufa refused, choosing instead to protect the sisters and fully embrace his identity outside the guild. This led to a direct confrontation where Kufa won but spared Vater. In response, Vater declared a formal manhunt against Kufa and his associates, permanently severing their relationship.

Throughout their interactions, Vater maintained a complex dynamic with Kufa, blending mentorship with ruthless pragmatism. Kufa occasionally referred to him informally as "the bastard father," indicating a fraught but familiar connection. Vater consistently prioritized the guild's objectives over personal bonds, enforcing its dictates even at the cost of losing a key operative.