Opal is Rukia's half-sister, they share the same mother. I also have decided to change Rukia's species from being a wolf-dog to half wolf and half hyena because i made more sense to me? Opal here is a wolf-dog though (so you can assume their mother is a wolf). Opal is more easy going than Rukia and not as easily annoyed, especially not by young children like Rukia.