|“||Two against one!! If that's the the case, let's confuse him with speed!!||”|
—Black Star, Chapter 7
The Ninja Sword (忍者刀, Ninjatō) is one of Tsubaki's Weapon forms, also sometimes known as Ninja Blade in the English dub.
Tsubaki's Ninja Sword form is not used by Black Star very often. This is most likely because her Chain Scythe form gives him a wider range of movements for attack and defense, and the Uncanny Sword form they attain later on is much longer and has more power than the short Ninja Sword. However, Black Star and Tsubaki can make use of the Ninja Sword form as a distraction when using Tsubaki's Dummy Star mode. Resonating with Tsubaki in Ninja Sword form also gives Black Star access to greater speed. Tsubaki uses this form in the fight against Mifune, and the fight against Masamune and in order to escape from Crona.
A more powerful and advanced form of this technique is Shadow Star: Third Form - Severed Shadow.