Board Thread:General Discussion/@comment-4957813-20131113141215/@comment-6007020-20140206205747

Shikai involves using the Spirit's power without forcing them to materilize in outside your Inner World, so it's perfectly feasable that while you can call upon your spirit for power, even if it's not present within you. Another thought I've had on the matter is that the Medallion doesn't steal away your Spirit, it just subjugates them into materilizing only for their new master.