Board Thread:Theories and Speculation/@comment-30241447-20170503042327/@comment-734582-20170503074433

Considering that Itachi only used it against either a stationary target or someone who couldn't see the attack coming and only used it in very specific cases, it can't possibly be as OP as some people think it is.

I don't think it can seal the ten-tails unless it's user is a being of equivalent power. Hashirama's gates could barely hold the beast. I think it makes sense that the Totsuka's blade simply scales with the strength of the owner.

As to the nature, it's likely a physical weapon. Keep in mind that Orochimaru was able to use his Kusanagi in his own jutsu e.g. Hidden Snake Hands could also summon smaller Kusanagi. So Itachi could simply have the weapon on him (sealed in his eyes or whatever) and then manifest it in his Susanoo.