Flip the switch and Ichigo is being executed instead of Rukia. However, before the Sōkyoku strikes him, killing him, a change happens. He's no longer Ichigo, but Zangetsu. Freeing himself from the bounds, he fights and wrecks havoc in the Seireitei. It's up to Rukia to help him break free from the one possessing him - if he lets her close enough to try, that is.