WARNING: The following contains spoilers for Season 1 of Onyx Equinox, now streaming on Crunchyroll.
Onyx Equinox has its fair share of tragic stories, from the sacrifice of protagonist Izel's older sister as an attempt to appease the gods to the warrior Zyanya losing her parents and entire village in a mass sacrifice due to the blood shortage. However, the most tragic might just be the tale of Mictecacihuatl and her former lover, Yaotl.
Born a human, Mictecacihuatl was sacrificed to the gods as a baby -- more specifically, to her future husband and God of the Dead Mictlantecuhtli. She was groomed to be his queen and to watch over the bones of the dead. As she grew, Mictecacihuatl wanted to become closer to humans and oversee their funeral rites, so one night, she traveled to the mortal realm and took part in a funeral service held by a small village. This is when she realized humans had emotions and feelings, and honored their dead.
Mictlantecuhtli initially denied her request to continue to tend to the funeral rites, but finally agreed as long as it didn't interfere with her duties in the Underworld. Mictecacihuatl lived among the humans and watched over their dead while also fulfilling her unwanted duties as a god. She eventually made her way to the city of Daniban where she took part in a sexual ritual -- and met the human warrior Yaotl.
Yaotl was to be sacrificed to Tezcatlipoca, to become one of his many celestial warriors. During his final year, Yaotl and Mictecacihuatl spent much time together and fell in love. Mictecacihuatl believed he would forget about her because of all the men and women who were being offered to him sexually. Yaotl argued against this and agreed to meet her in three days' time to prove he wouldn't forget her, even falling asleep while waiting for her return. They then agreed to meet again after Yaotl was sacrificed to Tezcatlipoca.
Mictecacihuatl waited for Yaotl to return, but it was Tezcatlipoca who met her. He chided her for meddling with his affairs and trying to steal his sacrificed soul, then blackmailed her into agreeing to leave Yaotl alone and never mess with the Celestial Gods again. Mictecacihuatl agreed, not knowing Yaotl was at the bottom of the very tower they stood on. She chased after them, but Tezcatlipoca wiped Yaotl's memories and made him an emissary, ensuring Mictecacihuatl would never be with him again.
Enraged, Mictecacihuatl swore to get revenge on the gods for taking her humanity and her lover. She tricked her husband Mictlantecuhtli into taking all of Daniban as a sacrifice, knowing the city was dedicated to Tezcatlipoca. She also knew of the bet that Tezcatlipoca and Quetzalcoatl had made, using it as ammunition for her quest in killing her husband. Because he was the one to make Mictecacihuatl a god, they share their power. He cannot harm her, and she cannot harm him. But by starting a "Holy War" with Tezcatlipoca, she hoped one of the other gods would kill Mictlantecuhtli for her so she could take control over his domain.
In exchange for not interfering in Quetzalcoatl's Champion's Quest, Mictecacihuatl could kill him if he was about to close the last gate, which would have cut off all her power. In the end, Izel didn't close the gate and Mictecacihuatl consumed her husband. However, she never got back the romance she wanted, as Yaotl turned her away after she restored his memories. Despite everything she did, Onyx Equinox's tragic villain still lost the one thing she loved most of all.