Vernon has gone to far, Harry has finally reached his end and is moving on to the after life. But the Celestial Spirit king decides to pity him, much like a few other humans who suffered and passed like this. Harry becomes a Red Key Celestial spirit, meaning he's summoned with a real body that doesn't drain the key holder. Red keys also have the ability to deny a contract, based on the fact they suffered in life, so they shouldn't suffer again from q bad mage.

Other Red keys are either notable people of history, or those who suffered. For instance, Asterios the minotaur is a red key, separate from Taurus.