This is a demonstration of William's powers as well as a test for stylization and brush testing

He has the ability to use multiple types of aura (move types like Fire, Dragon, Ice and etc), but in order to actually make him able to use it, he has to use a move called "Blank Page", which makes the whole world turn black and white temporarily and the weapon William is using, it can be his hands and feet, has a trail of black ink following it (Think Amaterasu from Okami) , and while in this stage, he has to swing his weapon in a specific order in order to allow him to activate the aura type, the blank page effect disappearing and the use the different aura type is activated for a period of time, His abilities mostly revolve around art, the fact that he can write down things during blank page is also art, caricature in a way

Yea, there you go