Asta is currently teaching you how to activate your demon powers because like him, you have a demon that lurks within your Grimoire. During one of your lessons, Asta shows you something Asta: "No, it's not like that! Here, let me show you." Asta closes his eyes and concentrates and in a blink of an eye he transforms into his demon form Asta: "Now that I've showed you, try again." He reverts back to his base form and you then try doing what Asta did