Ryoka (旅禍, Traveling Evil(s)) is the term the Gotei 13 use to identify those who are not aligned with Soul Society, either allies, rebels, intruders, deserters, or invaders. It is said that no good can come from Ryoka.
Main article: Ryoka Invasion
During the first Ryoka Invasion, Ichigo and his friends invaded Soul Society and were labeled as Ryoka. Their purpose for invading was the rescue of Rukia Kuchiki.
List of first Ryoka Invaders
Main article: Bount Invasion After the Bount broke into Soul Society they too were labeled as Ryoka. Their purpose was the destruction of Soul Society. While the former group also came into Soul Society at this time, they were no longer considered as Ryoka.
List of Bount Invasion Ryoka
Aside from these two, no other known groups have been classified as Ryoka, while there have been others that have committed actions against Soul Society that would qualify them as such.