Hardened Hearts (2018)

From the introduction: Thousands of years ago, four masters of magic and medicine-- Unko, Krow, Atua, and The Maniac-- served Salamander-kings as honored "Surgeons." Jealous of the Salamander-kings' power, the Surgeons developed a ritual to grant them immortality-- the prototype of lichdom. Carving out their own hearts, they created four Stones of Power: one each of Ruby, Hematite, Jaspar, and Aventurine. Once immortal, they lead sycophantic armies against the Salamanders. In a mockery of their title as Surgeons, they came to be known as the Butcher-kings. To combat them, the Salamanders created Zulfiqar, the Blade of Ultimate Destiny, a tool to steal their immortality. They first gave the gift to Krow as an offering of fealty. The instant Krow touched the blade, he was attacked and struck down. The Salamanders then killed The Maniac with Zulfiqar not through treachery, but brute force. But with the sudden death of two Butcher-kings, Unko and Atua knew that they were in danger. They had the blade stolen and locked the thing away in a temple, only accessible to one who held at least two of the Hearts. Knowing that the Salamanders would find another way to slay them, Unko and Atua abandoned their armies, left the Salamander Empire, and waited for another chance to rise to power. Over the years, immortal though they were, their magical abilities waned due to an imperfection in their ritual. They realized they would be doomed to an immortality of impotence. Atua sought release by attempting to find Zulfiqar and end his own life with the blade. He entered the temple of Zulfiqar, and was trapped there by a treacherous ward Unko had devised. Unko is said to have traveled far to the south, seeking out exotic new magics, searching for a way to enhance his immortality and reach true lichdom...