...Something has gone horribly wrong with the Shrine of Resurrection, so Link has died. In desperation, Princess Zelda reaches out through time and space to contact a magical con-man by the name of John Constantine, to hire him to take out Calamity Ganon, once and for all. Mr. Constantine agrees to this contract, in exchange for gold and jewels (not Rupees).

The terms of the contract:

I) The destruction of Calamity Ganon (the main job)

II) For every Divine Beast that is freed, there will be a generous bonus

III) Taking out the source of the Calamity (who is currently sitting under Hyrule Castle) will earn him a HEFTY bonus.

In order to maximize his chances, Zelda will teach Constantine about how Hyrule works in terms of magic and the supernatural, so he can use his talents to their maximum extent. He will also have as much prep time as he needs to get himself familiar with that world. Also, Constantine will have full access to the weapons of Hyrule, including the Champions' Gifts, assuming he can free the Divine Beasts.

(This will be a composite Constantine, because there is at least one version of him that basically has demonically tainted blood, so that would rule out the usage of the Master Sword as well as potentially the Light Arrows.)