He had taken you in thinking that you were just some random homeless orphan, he pitied you, so he took you under his wing in a way.

What he didn't realize, was that you had an ability that allowed you to gain one ability of someone else's permanently, which in your case, it was Chuuya's ability. Not even you knew about said ability

None of you had any idea about it, until It randomly popped up one day, and you had locked yourself in the room Chuuya had given you at his place, and Chuuya, being slightly concerned, attempts to check up on you