Diseum von Earlshide reigns as king of Earlshide Kingdom. He presents as a middle-aged man with golden hair, a mustache, and emerald-green eyes, consistently attired in high-quality clothing that radiates style and authority. His personality displays a relaxed demeanor and preference for informal interactions, famously insisting Shin Wolford address him as "Uncle Dis" due to viewing Shin as a nephew-like figure. This sociable, approachable-uncle nature coexists with serious discussions during visits with Merlin. His son August inherits these traits, including playful manipulation and prioritizing individual merit over social status. Diseum attended the Advanced Magic Academy, participating in the first recorded devil subjugation where he witnessed military devastation and faced mortal danger before Merlin and Melinda intervened. This forged their lasting friendship. Post-graduation, he abandoned his Crown Prince position to accompany Merlin and Melinda on a vagabond journey, during which they treated him as an apprentice or "maid"—an experience his fiancée Julia von Earlshide reportedly never fully accepted. As monarch, Diseum recommended Shin’s Magic Academy enrollment to address Shin’s lack of common sense, stipulating protection from political exploitation. He maintains key relationships: familial bonds with Shin, trusted alliances with Merlin and Melinda despite their past dynamic, and ties to Julia, his fiancée during his princely era. His leadership champions capability over nobility, a principle his son August upholds. Magically, Diseum holds above-average capabilities as an academy graduate, though specifics remain undefined.