>>19739327Warning possible The World Ends With You spoilers:
Joshua would win, with Ash being the corner stone of success, Ash thought he was saving the world when in fact he defeats the people trying to save the world, all while Ash believes Joshua is his friend.
Of course Joshua would offer the battle, while raising the stakes and with Ash still reeling from the whole "I used our friendship to use you as a pawn in my scheme for world domination and you gladly followed", I'm not too sure how it would end 