Board Thread:Questions and Answers/@comment-3459763-20140421035831/@comment-8986886-20140421154352

The Shihakushou of Tensa Zangetsu seems to reflect Ichigo's Reiatsu, (remember how it changed when he used Saigo no GT, and again during the Fullbring arc) meaning it also evaporates as Ichigo's Reiatsu is depleted. Similar to how the wings of Daiguren Hyorinmaru can regenerate, as long as there is water around, Tensa Zangetsu's Shihakushou will always regenerate as Ichigo's Reiatsu is restored.