Daniel exists as a supernatural entity, serving as the constant companion and familiar to a central shinigami figure. He typically appears as a sleek black cat capable of speech, distinguished by bat-like wings and a bell worn around his neck; this bell emits a ringing sound perceptible to living humans, signaling his or his companion's presence. Notably, his physical form takes human shape in the live-action television drama, manifesting as a young boy instead of a feline.

Functionally, Daniel assists in guiding departed souls towards the afterlife and frequently intervenes in human affairs alongside his shinigami partner. He possesses the ability to alter his appearance, demonstrated when he temporarily transforms into a young boy to guide someone during a treasure hunt. His personality presents a calmer, more reserved counterpoint to his companion's empathy, showing less overt sympathy towards humans while maintaining patience during their interactions. Despite this detachment, he actively mediates between the living and the dead, facilitating final communications and helping fulfill unresolved wishes.

Daniel shares a history with another supernatural familiar named Nicol (Nicolas), companion to the shinigami An; the two were once close friends prior to their respective bonds with their shinigami partners, establishing personal history beyond his duties.

Across adaptations, Daniel's core role remains consistent: he provides grounded perspective during supernatural interventions, offers practical assistance in soul guidance, and acts as a sounding board for his companion's emotional responses to human struggles. His arrival often heralds impending supernatural activity, with the distinct chime of his bell serving as an auditory herald to significant events concerning life, death, or emotional resolution.