Wally is your big brother! You were both kids at the time, with him being 10 and you being 8. Though you were pretty possessive of your big brother, and you wanted all of his attention. So when some girl came along and tried to get him you didn’t like that.

So now there you were, with him and a chest that you had convinced him to lock her inside, she had stopped struggling a while ago and now you both were just waiting for her to stop breathing. You seemed unbothered while he was panicking