Hōgyoku

The also referred as The Orb of Distortion, is a small orb that dissolves the boundary between a Shinigami and a Hollow. It can allow a Shinigami to use Hollow powers and vice-versa, allowing the user to tap into a vast amount of spirit energy. The Hōgyoku was the end result of an experiment by the Soul Society's Department of Research and Development. After some through testing, the developer of the Hōgyoku, Kisuke Urahara, foresaw the dangerous nature of his creation. Out of fear of what people would do with the Hōgyoku, he erased all the data about how it was created. Shortly thereafter, he was terminated from the Soul Society for creating it. This item lay dormant in the untraceable Gigai that Rukia was in during the Soul Society arc of the manga and anime.Sōsuke Aizen found two ways for the Hōgyoku to be removed from its host. One, the soul gets burnt away with extreme heat, hence the use of the Sōkyoku. Two, the Hōgyoku is extracted through artificial means, through the use of a specialty device developed by Urahara. His first plan was to allow Rukia to be put to death on Sōkyoku Hill, and retrieve the Hōgyoku afterwards. That plan changed when Ichigo stopped the execution. So he had to plan for his next course of action, and uses Urahara's device to extract the Hōgyoku. As Sōsuke Aizen reveals to Orihime Inoue, The Orb of Distortion was still asleep when he stole it. It needed time to mature and awaken before it could be at its full potency. Through his research though, Aizen found out that through the infusing of his spirit power, the Hōgyoku could be forced into a state of readiness which he could work with while it is in a dormant state. With it, he was able to create powerful Hollow/shinigami hybrids called arrancar and rose an army to subplant Soul Society. He claims that he brought Orihime to Las Noches to repair the Hōgyoku and use its full power, but has yet to complete this task. Later, he claims that he used Orihime brought her to lure her friends, namely Ichigo and the others. This was to weaken Soul Society's forces during the battle of the fake Karakura Town.