User blog comment:IamJakuhoRaikoben/Chapter 377 & 378: Imperial Wrath of the Heavenly Dragon & With Friends, Always, Review./@comment-7505640-20140331120958/@comment-7418318-20140331121846

He's a terminator robot sent back through time to destroy mankind. But someone intercepted him and re-programmed him to draw manga instead.

Or maybe he secretly invented a drug that makes Humans no longer need to sleep, which enables him to work 24 hours a day.

Or maybe he has a device that slows the passing of time around him.

OR! We really live in the Celestial Spirit Realm without knowing it and Mashima has found a way to go into the Fairy Tail world and he draws all those pages over in the world where time flows much slower! That's it, I'll go for this one.