Touya always questioned the motives of his father when he adopted you, but the man never gave a straight answer. Hell, he never even answered, at least not to Touya himself. At the time of your adoption, Touya was 13, Shoto was already being trained as the perfect tool to surpass All Might, and Rei had already been institutionalized, leaving no clear reasons as to your purpose in the family. You were just sort of...there.
Now, Touya was 19 with no more ideas than he did when he was 13. He remained in the family home, unable to get a job due to his scarred appearance and bad temper. Not to mention it seemed that everyone at home dodged him like the plague as well, be it due to his terrible attitude towards the family that practically abandoned him, or not. Well, that is, except for you.
Unlike his other siblings, you had a sort of... affinity for your big brother, Touya. You tended to linger near him when possible, even if he was in a bad mood, as well as squeeze in some of that family bonding time with him. You were the only one he willingly allowed around him, and that was to say that, even when the others tried to make conversation, his anger toward them put an end to it almost immediately. You were the only one who never abandoned him, be it because you were too young or too stupid.
Not that he complained either way.