Servant of the Underworld by Aliette de Bodard

It's one reason Human Sacrifice is 100% tolerated-unlike in real life, it actually keeps the Empire running, and holds back the end of the world. All the magic and spells in the series require some form of sacrifice to complete.

Better the Devil You Know: Sure, Tizoc-tzin is obnoxious, incompetent and paranoid, but the alternative would be having star-demons wreak havoc in the Fifth World.

Ichtaca basically runs the temple and even attends to Acatl's duties at court, and wishes that Acatl really would put more effort into being the High Priest instead of just acting like any other priest of the Dead.

Beleaguered Assistant: Ichtaca, the temple's fire priest, to Acatl.

Aztec Mythology: The main character is the High Priest of Mictlantecuhtli.

Obsidian Shards, the first story Aliette de Bodard wrote in this universe.

There are also three short stories set in the same universe and starring Acatl. One of those sacrifices dies of a magical illness, and Acatl has to find out why.

Master of the House of Darts: The coronation of the new emperor has failed, and there's barely enough sacrifices to hold off the apocalypse.

Once again, Acatl is charged with mystery solving, only this time he has to do it while trying not to be eaten by demons.

Harbinger of the Storm: The Emperor is dead, demons have overrun the empire, and to top it all off, a councilman has been murdered-one of the councilmen tasked with choosing the new Emperor.

Things get complicated as Acatl finds himself embroiled in court politics. Traces of powerful magic fill the place, and Acatl is called on to find the missing woman.

Servant of the Underworld: Acatl's brother is found in the empty room of a missing priestess, covered in blood.Notable for being fantasy novels not set in some version of medieval Europe, but instead in the Aztec Triple Alliance at its height of power. It concerns the adventures of Acatl, High Priest of the Dead, as he tries to solve a series of murder mysteries in Tenochitlian, the capital of the Aztec Triple Alliance. Obsidian & Blood is a book trilogy by Aliette de Bodard.

Servant of the Underworld by Aliette de Bodard