When he transformed, William felt something different about his spirit. He felt a connection with something far, far away from him, like some sort of a bond. He didn't need to think deeply about it, knew this was something related to that Mystic Art he did, the connection with that spirit.
In the meantime, he tried to walk in the transformation form, ending up feeling exhausted weirdly after five hours every time.
He tried to look for the reason, and he spotted it on his fourth attempt. It felt like if he transformed and did nothing, didn't fight or anything, his spirit power would deplete in five hours! It was new, strange, and yet quite alarming.
That made him try to fight something. As Sloth didn't accept his request to train, asking him to not waste time and keep heading fast towards the continent, he decided to try fighting the ocean monsters every time they passed a trait.