Board Thread:General Discussion/@comment-20311922-20130916143753/@comment-4161952-20130927213142

If Ichigo survived Byakuya's Senkei, it isn't guaranteed that the technique will kill every time. Whoever he used it on is still alive.

Only someone with monstrous defense and endurance can withstand Senkei. Maybe he tested it out on his own Zanpakuto?