The King of Creation is a title given to the one whose will would essentially stand above all others. He would have the power to create the world any way he sees fit, and would govern creation. This individual was revealed to be Ginji Amano.
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Once all worlds were returned to zero - a blank slate, there would only be the Creator . However, Ginji already had it made up within his mind that he wanted the world in which he knew. He wanted a world in which all of his enemies existed, all of his friends, and everyone he didn't even know.
Through Ginji, everything was created from nothingness. Seeing that Ginji was above all others, and by the presence of the Infinity Fortress and Makube (and the fact that he wanted all of his enemies and the people he didn't even know to exist), it can be accurately assumed that his will alone dwarfs that of the Archive and Makube (seeing that he created them, which in essence would create all of the realities that the Archive established). However, seeing that his will was the absolute will, he believed that the other world was merely a dream, so in truth, it really was.
Before the events of the Ginji becoming the King of Creation, Sarai Kagenuma explained that Ginji would be able to do whatever he wished, and create whatever he wished.