Later, when they were alone together in the grand, empty mansion, Byakuya told Rukia the remainder of the truth, one too shameful for outsiders’ ears. Then he turned away from the woman who bore the face of the one he had wronged all those years ago, the burden of guilt beyond what he could bear.

Yet she remained at his side, his sister—never anything more, for he had so sworn—an eternal reminder of his ancient sin.

Her forgiveness could never be earned, only granted, but even should she ever do so he wasn’t certain he could forgive himself.

Unnecessarily Long and Tiresome Authoress’ Notes:
Hard to present what my actual idea is in 100 words, but I hope I’ve left enough clues for everybody to put two and two together.