Before Rukia's execution, Jushiro Ukitake took some time breaking the seal on an item which was later used to destroy the Sokyoku.
When Ichigo arrives to save Rukia he is wearing a cape which allows him to fly which Soifon comments during her fight with Yoruichi that the cape came from the Shihoin clan, Yoruichi's clan.
They both have the same insignia on it and I recall when Ukitake appeared with the shield thing someone commented that it had the Shihoin clan symbol on it.
But why does Jushiro Ukitake have it? Shouldn't it be with the stealth force or even Yoruichi's possession? Better yet, since it is able to destroy the Sokyoku, why is it entrusted to another captain rather than Head Captain Yamamoto?