Board Thread:General Discussion/@comment-6057702-20130807105845/@comment-8986886-20130807142304

In order to regain his powers, lost after using the "Letzt Stil", a Quincy's body and spirit must be pushed to their outmost limit. While in that state, he must be shot with a spirit arrow, exactly 19mm to the right of his heart; as seen in the ending of ep126.

Since Ichigo still has his Quincy powers, Mugetsu couldn't have been his "Letzt Stil", but there are certainly similarities between the two techniques.