Aizen's betrayal at the end of the Soul Society arc is a standout moment in Bleach's history. Aizen's mastery of Shunpo, Hakuda, and swordsmanship makes him one of the strongest characters.
Shortly after that, a familiar Spiritual Pressure crushes those creatures in Bleach TYBW episode 31. Rukia Kuchiki is horrified, as Sosuke Aizen enters the Seireitei. The Soul Reaper feels it's ...
well over a hundred years before the main Bleach story. As a young and talented Shinigami, Aizen turned his scholarly mind to exploring the mysterious boundary between hollows and soul reapers.