|Alternate Title(s)||Enchanted Blade (Funimation Dub)|
|Demon Weapon Data|
|Human Form|| Masamune Nakatsukasa|
|Manga Debut||Chapter 6|
|Anime Debut||Episode 10|
The Uncanncy Sword (Enchanted Blade in english dub) is a powerful demon weapon used by the Nakatsukasa clan that was inherited by Masamune Nakatsukasa, while the bulk of the family transformations were inherited by Tsubaki, as though the latter deserved it more for reasons unknown. After defeating Masamune, Tsubaki acquired the Uncanny Sword transformation, thereby obtaining all the abilities that come with it.
Tsubaki is wary in employing the Uncanny Sword mode for Black☆Star, since its demon blade nature could lead to devourment of his own soul, if overused. Only a few limited uses of the form demonstrated just how significant the strain that it places upon his body is, especially on his heart, causing Black Star to grasp his chest and nearly collapse after only moments of use.
When Masamune had the transformation, the Uncanny Sword was known for it's ability to possess the souls of others and take control of the possessee's body and, later, eat the soul. However, once Tsubaki gained it's transformation, she chooses not to utilize this ability, The sword also houses the entity, The Will of Nakatsukasa.
The Uncanny Sword takes the form of a katana with a black blade and a bandage-wrapped hilt.
- It was initially speculated that the presence within the sword belonged to Masamune, Tsubaki's brother but later chapters have suggested otherwise. Firstly, Masamune appears with the darkened faces of the others that have been consumed, seemingly making him just another victim of the sword. Also; the entity refers to itself as "we", suggesting it is composed of all the souls it has collected since it's creation, rather than having just a single identity.
- It is unknown at this point if this entity is similar to the Little Ogre, located within Soul's soul.
- The name "Uncanny Sword" may stem from the concept of the "Uncanny Valley" wherein a person's acceptance of something drops if it looks vaguely but not quite human. Since this is a dangerous mode that changes Black Star's face and makes him more demon-like, it is possible the name derives from the concept.