It was an accident... Seriously!-

You're a witch and you accidentally made a deal with a demon... Don't ask her how she came to make a pact with Scaramouche, but after that Scaramouche promised you total loyalty to you, no matter what

She was on a mission with Scaramouche by her side, knowing that Scaramouche can't look you in the eye directly, because if he removes the blindfold, he's capable of turning into a demon killer... To the point of being able to kill its own owner