After Gravis was done with forging his equipment, he didn't have much else to do. His future tempering would come to him by itself, and he didn't have to search for it. Now, he only needed to spend his remaining time as productively as possible.
So, Gravis simply split himself in two for one simple reason: Law comprehension. He remembered the picture of Manuel that he had received on his birthday and also remembered the name of the sixth Realm, which was also called the Law Comprehension Realm.
In Manuel's picture, Gravis had seen him sitting inside a massive storm. Gravis was pretty sure that Manuel was thinking about some kind of Law and trying to understand it. Gravis also knew that, at some point, he would probably need to do that too. After all, the comprehension of Laws would definitely become paramount in the future.