Board Thread:Theories and Speculation/@comment-25227224-20150323110334/@comment-2005101-20150417171424

It could be interpreted that the edge of Sasuke's Kusanagi no Tsurugi was particularly sharp, as even before he enchanted it with Raiton he claimed that Sai's way of defending against his blade was appropriate. I think it's important to take note of the blade's durability as well, considering how long it has been kept in immaculate condition despite coming out of something like Deidara's C0.

That said, it was mostly a useless accessory that was either lost or used against him in almost every fight. Of the three types of Kusanagi no Tsurugi, his was the only one with no special properties beyond its dangerous edge, which was only undermined because of Chidorigatana. It should've been capable of levitating and transforming like Orochimaru's; I used to hope that those were techniques applied to the blade, rather than inherent traits like the Totsuka no Tsurugi's Fūinjutsu.

But regardless of how comparatively useless it seems, it's still officially classified as a type of Kusanagi no Tsurugi.