Thief serves Prince Beelzebub as royal adviser in Sand Land's demon territory, using his thieving expertise and strategic wisdom to ensure demonkind's survival. He adheres to a philosophy of taking only necessary resources, stealing water from humans without excess to sustain his people while striving to coexist relatively peacefully. This pragmatic approach reflects a nuanced understanding of survival in the desert wasteland.

Recruited by Beelzebub to locate the legendary Phantom Lake, Thief joins Sheriff Rao and the prince, forming a trio confronting the human king's army. He operates their tank during vehicular combat, alternating driving duties with Beelzebub and contributing tactical insights against royal forces. His experience and cautious nature often counterbalance Beelzebub's impulsiveness, with his thieving skills proving vital for bypassing obstacles and securing essential items on the journey.

Thief demonstrates loyalty and protective instincts toward Beelzebub, acting as a guardian during their travels. He participates in uncovering mysteries around Sand Land's water scarcity and the king's tyranny, witnessing Rao's revelations about the war's true causes. His presence adds comedic elements through group interactions, particularly during tank operations and moments highlighting generational friction with the younger demon prince.

Following the Sand Land mission, Thief continues accompanying Beelzebub and Rao into Forest Land, an expanded narrative arc featuring new environments. He remains integral to the core group as they encounter Muniel, a wingless angel, and Ann, a human mechanic skilled with vehicles, adapting his skills to unfamiliar challenges in this lush region. His role persists through subsequent conflicts and explorations beyond the original manga's storyline.