Huehuecóyotl originates from Aztec mythology as a god linked to music, dance, mischief, and song, embodying the trickster archetype who creates chaos to alleviate boredom, often by instigating conflicts among humans or other supernatural beings.

Classified as an "Another" within the series, this deity exhibits an unpredictable, childlike demeanor driven solely by a desire for entertainment, frequently disregarding collateral damage or moral consequences. Physically, Huehuecóyotl appears androgynous with long black hair and distinctive golden or amber eyes reflecting their otherworldly nature.

Centuries before the main events, they formed a complex relationship with the Japanese occultist Abe no Seimei, who bestowed the Japanese name "Kohaku" (meaning "amber"). This name endures among characters, symbolizing their tumultuous connection to Seimei’s legacy. Huehuecóyotl later identifies Arata Miyako, Seimei’s reincarnated descendant, frequently engaging with him while calling him "Seimei." Their interactions alternate between playful teasing and creating dangerous situations designed to test or amuse Huehuecóyotl.

Their actions directly influence key storylines, such as orchestrating a ritual using World War II corpses to provoke Arata, or overlooking the demon Azazel’s crimes despite awareness of the suffering, justifying inaction by prioritizing personal amusement. This indifference sparks confrontations with Arata, who challenges their detached perspective, though Huehuecóyotl remains largely unchanged, maintaining their role as an agent of chaos with skewed priorities. Their presence underscores themes of reincarnation and ancient bonds while serving as a catalyst for conflicts that test the protagonists’ resolve and ethics.