In Bleach's Soul Society arc, Ichigo and his fellows beheld the mythical Soul Society for the first time, and the gang fought their most intense battles yet to save Rukia as the Soul Reapers rushed to defend their homeland. The arc is beloved for its action, but its impact on the story and characters is even more significant. The following five major plot twists altered the course of Bleach forever.
When Yoruichi Revealed Her True Form (& Sex)
Ichigo had an odd friend named Yoruichi, a talking black cat who knew the Soul Society like the back of his paw. Yoruichi was also a friend of Kisuke Urahara's, and he gladly volunteered to help Ichigo and his friends infiltrate the Soul Society to rescue Rukia from twisted justice. Yoruichi was stronger than he looked, and at some point, he had dragged Ichigo to a safehouse, and Ichigo wondered how on earth a housecat had carried him there.
There, Yoruichi revealed a secret: "he" was actually a she, and a former Soul Reaper at that. Yoruichi was a well-built young woman with incredible athletic abilities, who had gone rogue from the Soul Society years ago. Now, Yoruichi would fight with Ichigo and his friends in person, first clashing with her former student Soi Fon, then facing off against the Espada Yammy Llargo in the next story arc. The "talking cat" gimmick was over. It's time to fight.
When Rukia's Role In Kaien's Death Is Revealed
Ichigo and his friends met Kukaku Shiba and her younger brother Ganju, both of whom belonged to the noble Shiba family. But there used to be a third sibling, the popular Kaien Shiba. Soon enough, Ichigo learned through Ganju that Rukia had killed Kaien with her own two hands, and Rukia was still wracked with guilt. After her rescue, Rukia approached Kukaku and gave her a heartfelt apology, and Kukaku graciously accept it and urged Rukia to move on.
Rukia was glad that the Shibas didn't hate her, but she has not yet forgiven herself. Rukia's role in Kaien's death was now established, and it would factor heavily into Rukia's future battle against Aaroniero Arurruerie, who would use Kaien's likeness, powers and memory against her. Without this reveal, the Rukia/Kaien backstory wouldn't have been nearly as impactful.
When Renji Abarai Switched Sides
For a time, Rukia was the only Soul Reaper on friendly terms with Ichigo, and her friend Renji Abarai was determined to uphold Soul Society law and defend Rukia's execution. Ichigo and Renji came to blows over Rukia's fate, and after Renji narrowly lost to Ichigo, he had a change of heart. Renji thought back on his and Rukia's childhood days together on the streets, and that, combined with his inability to uphold Soul Society law, inspired him to change his priorities.
Renji decided then and there that he valued his friendship with Rukia more than anything, and he implored Ichigo to save Rukia, no matter what. This would put Renji on a course to face Captain Byakuya Kuchiki and, in the process, practice using his bankai. After the Soul Society arc ended, Renji continued to fight as Ichigo's ally.
When Ichigo's Inner Hollow Manifested
Ichigo's body hid a secret: an inner Hollow that was the incarnation of bloodlust and gleeful chaos. A few times in the Soul Society arc, that inner Hollow protected Ichigo with a bony mask, confusing Ichigo and Yoruichi alike. Then, when Ichigo fought Byakuya Kuchiki and nearly lost to him, Ichigo's inner Hollow decided that enough was enough. The inner Hollow could think and act for itself, and it assumed control of Ichigo and turned the tables on Byakuya.
This immense power was enough to force a draw against Byakuya, and both fighters were shocked that such a monster had appeared at all. Ichigo hoped that the matter was resolved, once he tore off his strange mask, but not so. In the next arc, Ichigo would have to face his inner Hollow again, and either conquer it or be a slave to its power for all time.
When Sosuke Aizen Outed Himself As A Traitor
This was not only the most impactful plot twist in the Soul Society arc but possibly the biggest in the entire franchise. Something seemed off during the entire Soul Society arc, and Captain Toshiro Hitsugaya could smell it. He and Rangiku Matsumoto dived deeper into the mystery of Captain Aizen's untimely death, and Hitsugaya was aghast when he found all of Central 46's members dead at their desks.
Then Aizen appeared at Rukia's execution site and extracted the Hogyoku from Rukia's chest, and declared his intention to form an Arrancar army and rule all of creation from the empty throne in the heavens. Ichigo and the Soul Reapers tried to capture Aizen and his co-conspirators Gin and Kaname, but they were too late. Some Menos Grande appeared, and beamed Aizen and his allies up to Hueco Mundo, far from the Soul Reapers' grasp. A new enemy had appeared, seriously raising the stakes. Who could possibly stop Sosuke Aizen and his Hollow army?