Yhwach is the father of Quincy and the ruler of Wandenreich, going by the moniker “A” – “The Almighty.” He is the leader of the Sternritter and the Soul King’s son. In addition, he organized the Quincy rebellion against the Shinigami. Yhwach, one of the series’ strongest characters, is rumored to be virtually unbeatable. But much before the beginning of the story, Yhwach had been killed by the previous generation of Gotei 13. Here is how he came back to life.
Shinigami VS Quincy
Both the Shinigami and the Quincies hunted down Hollows. While Shinigami were souls, Quincies were actually humans. Although both of them had the same goal – to hunt down Hollows – their ways of doing so were completely opposite. The Shinigami sent the Hollows to Hell so that their souls reincarnate as humans in the next life. But the Quincies killed the Hollows’ soul, eradicating it completely, and ensuring that it doesn’t reincarnate.
This was completely against the Shinigami’s rules and purpose. It also went against the laws of nature and created an imbalance among the souls of the world. Since the Quincies’ inception, the Soul Society spent a lot of time trying to convince them that dealing Hollows should be left to the Shinigami. The Quincies resisted accepting the circumstances. The Shinigami were forced to grudgingly eradicate the Quincy in order to preserve the harmony of the planet as the number of Quincy grew and the cycle of souls became more unstable over time.
This led to a war between the Shinigami and the Quincies. The Quincies were led by Yhwach and the Lichtreich, who fought the original Gotei 13. But the Gotei 13 defeated Yhwach and all of them were killed. But Yhwach had the chance to come back to life due to a prophecy among the Quincies.
The Quincies have a legend that originated as a song. This song was called Kaiser Gesang and was about a sealed king. The song predicted that after 900 years, the seal will be broken and the monarch would regain his heart. His mind would resurface 90 years later. And his power would come back 9 years later. Yhwach further added to it by saying that 9 days later, he would conquer the world.
He was able to come back to life with one of his unique powers, which is called Auswählen. Yhwach can forcibly steal the power of other Quincies as an extension of his capacity to disperse portions of his soul to others. 9 years ago, he utilized this method to reclaim his power during his revival. Yhwach chose the Quincies he believed to be impure, including those that are mixed blood, and then take their powers and use them for himself. Victims of this process die as a result of it, especially the weak.