As the episode explores Ikkaku’s past in the Rukongai, a timeline appears to map his journey:

: Mentions that Ikkaku is one of the few non-Captain Soul Reapers at this point in the series capable of Bankai. Technical Implementation Zaraki Division's Secret Story! The Lucky Men - Bleach Wiki

: A visual "Lock" icon explaining that Ikkaku keeps his Bankai hidden so he won't be forced to leave Squad 11 or become a Captain.