Originally Posted by
Petrikow
Though as a side-note, since the official translation sort of doesn't quite address it:
As I alluded to in my post, what he's doing is transferring something called 運命力 ("Fate Power" and you'll have to excuse the Japanese, because this term doesn't have a commonly accepted translation). This is explained earlier on in Babylonia as a resource that signifies how long one is fated to live. A way of counting one's fortuity towards living, if you will. Fou gave up all his own so that Mashu could live. Thus Fou ceased to be the impending Beast IV, and was rendered a harmless critter.