Onyx Equinox begins when the Aztec god of the underworld, Mictlantecuhtli, levels a Zapotec city after stealing blood sacrifices from the other gods. This prompts god Quetzalcoatl to close the gates to the underworld. However, he can’t due do this due to said gates being made of obsidian, which is toxic against the gods. So instead he makes a bet with Tezcatlipoca: he will find a human, “the lowest of the low”, and crown one his champion so they will close the gates before the equinox, when Tezcatlipoca will kill off humanity.
The chosen is young Izel, who is forced to discard his apathy toward his fellow man and prove humanity’s potential. Soon Izel’s epic journey will take him across ancient Mesoamerica to save humanity from a war between the gods…