The Ryoka Invasion was a major conflict detailing the first time Ryoka had ever gained ground against the elites of the Soul Society. It was an invasion by Ichigo Kurosaki, Yoruichi Shihōin, Uryū Ishida, Yasutora Sado, and Orihime Inoue into Soul Society to save their friend, Rukia Kuchiki from being executed.
The Invasion started when Ichigo and his friends decided to save her from an unjust fate that was Ichigo's fault more than hers. They proceeded to go into the Soul Society itself, immediately causing a stir that created a level of distrust among the Gotei 13, fracturing it with the seemingly impossible death of one of their own, Captain Sōsuke Aizen, which was blamed on the Ryoka invaders.
The Invasion ended with the amazing defeats of various captains and lieutenants at the hands of Ichigo and his friends, but it quickly became even further complicated when a vast conspiracy was revealed to have manipulated the entire Gotei 13. Sōsuke Aizen was not only revealed to be alive, but the mastermind behind the whole conspiracy, with Captains Gin Ichimaru and Kaname Tōsen acting as his subordinates. The major goal of Aizen was a creation of Kisuke Urahara, called the Hōgyoku, that had been hidden in Rukia's body. Now in hand, he escaped, leaving the Gotei 13 to ponder the next move.