Urahara Was a Captain Before He Was the Man Under the Hat
SPOILER!
Episodes 206–207 · 110 Years Ago
The Past arc rewinds Soul Society far enough to show familiar adults occupying completely different positions. Urahara becomes captain of the Twelfth Division, Hiyori is his suspicious lieutenant, and the institution that later exiles him still looks intact. The flashback matters because it turns Urahara from mysterious mentor into somebody who was once inside the system Aizen eventually exploited.