I totally suspected Byakuya was playing a long game, but when he finally turned on Muramasa to go after Koga, that reveal really hit me with a sense of "ah, so this was his plan all along," and the animation during their duel was just breathtakingly good, honestly some of the best I've seen. Plus, getting all that specific history about the Kuchiki family and Ginrei in a filler arc felt like a dramatic, unexpected bonus, giving me a deeper understanding of their lineage.