Board Thread:General Discussion/@comment-27140233-20151109022617/@comment-1387259-20151112161350

"Filler" or "not-canon", were things not created by the author of the manga. Muramasa is a filler character. Amagai is a filler character. Nozomi is a filler character. Ashido Kanō is a canon character who first appeared in a filler episode. The spirits of Katen Kyoukotsu are (as we've learned within the past few weeks) canon characters that first showed up in a filler arc. There is most certainly a difference. This site is more than just forums. There's plenty of informative articles. I'd suggest reading them.