|“||We will answer your call. Once only, when you need us, destruction, waste, carnage shall answer. We shall complete your cure.||”|
Makhai are spirits of battle and combat. It was initially believed that the makhai were chained by the Spartans in order to keep the spirit of war in their city, but Piper McLean discovered that the makhai's power was not to be unleashed unless fear has been felt before. The makhai were one of the ingredients needed to make the physician's cure.
Makhai are fiery spirits that manifest as a whirlwind of emotions: hatred, bloodlust, fear, and also love. While they were still kept in the statue of Ares, the makhai's presence was felt through a "low metallic pulse", hence why they are sometimes called the "chained god's heartbeat".
After being captured and brought aboard the Argo II, Nike exclaims that one of the Seven will die battling Gaea, their only hope of surviving being the physician's cure. She mentions one of the ingredients to be "the chained god's heartbeat in Sparta" which refers to the Makhai.
After retrieving the Pylosian mint from his relatives, Frank Zhang explains that the chained god they're looking for is Ares, more specifically, a statue of Ares kept in Sparta. Piper McLean and Annabeth Chase volunteer for the mission, and upon entering the Temple of Fear housing the statue, they encounter the giant Mimas. Unable to face him using reason, Piper teaches Annabeth how to fight Mimas with emotion instead.
During the fight, Piper realizes the true reason as to why the Spartans had the Makhai chained. Praying to Phobos and Deimos, her half-brothers, Piper offers up her cornucopia as a sacrifice and uses it to take off the head of Ares' statue, releasing the Makhai. They inform Piper that she can call on them once before disappearing.
Later, when presenting Asclepius with the ingredients of the physician's cure, Piper summons the Makhai.