Using an ancient dimensional gate built beneath it by the Olmecs, Mictlantecuhtli, Lord of the Underworld, attacks the city of Dani Baán, stealing its blood sacrifices from the gods and wiping out its populace.

To that end, they entrust Quetzalcoatl to close the five gates to the Underworld situated in various locations around Mesoamerica, cutting Mictlantecuhtli off from further theft of their divine sustenance.

Suspect of his intensions due to the latter's manifest family ties in the Underworld, Tezcatlipoca informs Quetzalcoatl that he intends to destroy this era of humanity on the following equinox, but Quetzalcoatl coerces him into a wager: unable to directly work the Olmec obsidian gates himself as they are repellent to gods and mystic beings, he will choose the "lowest of the low" among humans to close them all instead before Tezcatlipoca's deadline.

[12] In January 2022, Alexander revealed that the budget of Onyx Equinox was "near 1/3 of a lot of western shows" and said a main reason they unionized was because she "threatened to leave before production started."

[13] In May 2023, Alexander reported that Crunchyroll couldn't find production assets for episodes 4-12 of the series because of "how they archived it" and said she never made copies because "it wasn’t allowed.

[16] Ederlyn Peralta of CBR said that the series is unique, with "mesmerizing and highly-detailed character designs for the gods" of Mesoamerican culture and noted that while it is an adult animation, due to the "gore, profanity and sexual content," it, in their opinion, fails to have "quality character development for Izel and his comrades," and reported that some viewers believe that the protagonists are annoying and unlikeable because of their "whining.

"[19] Raye Rodriguez, the creator of High Guardian Spice, recommended the series, calling it a "dark adult animation" which has "unique storytelling," beautiful music and art, and encouraged his followers to help it get a second season.