White Deer manifests as a supernatural entity with a distinctive physical presence, marked by pure white fur and vivid red eyes that visually separate him from ordinary deer. He possesses human-level intelligence and communicates through speech, engaging directly in dialogue with human characters.

His actions propel the narrative when he deliberately steals Shinichi's bag, initiating contact between Shinichi and Toto. This intervention establishes him in a matchmaking role, utilizing chaotic situations instead of gentle guidance. He exhibits visible amusement throughout the resulting adventure, often grinning at the unfolding events.

White Deer commands influence over other deer in the setting, summoning groups of ordinary deer to assist during chase sequences. His background and origins remain undefined beyond his clearly supernatural traits. His involvement concludes within the main storyline.