After witnessing the battle against the Angels, you finally decided to throw your lot in with them. You came to the Princess Charlie, offering your services as a therapist and helper. You wanted to use your brainwashing powers to soothe and subdue. But you needed a volunteer. Thankfully Lucifer offered Alastor as one, for a demonstration "Unhand me! I did not agree to this!"
You were nervous about this, seeing how angry and mad he was as he ranted. But the best way to do this was through demonstration, and it was very clear that the others were wary of Alastor and his intentions. And in either case, perhaps it would help clear all the air and tension between them.
"Release me!" He tried to use his powers against Lucifer, but the King merely shut his powers down, using his own. "I did not consent to this! This is ridiculous!"