The Uncanny Sword (妖刀, Yōtō) is a demon weapon form transformation passed down by members of the the Nakatsukasa Clan. Masamune Nakatsukasa had inherited this transformation from his ancestors. After his death, the Uncanny Sword is then absorbed by his younger sister.
After gaining the transformation, Tsubaki is capable of changing to this form via Tsubaki Mode Change: Uncanny Sword (椿のモード変化「妖刀」, Tsubaki no Mōdo Henkō "Yōtō").
The Uncanny Sword takes the form of a katana with a black blade and a bandage-wrapped hilt. In the anime, the Uncanny Sword's true form is expressed.
Soul Possession (魂憑依, Tamashī Hyōi): One of the Uncanny Sword's known abilities is "Soul Possession", in which exploits the fears in people's hearts to possess the body and soul of the person who carries it. In the end, it absorbs the person's soul entirely. The appearance of the individual changes; they gain black lines around their face. Those possessed also take on red eyes.
Shadow Manipulation:The Uncanny Sword also can control the shadows of its host.
True Form: In the anime,
The Uncanny Sword cannot control two soul wavelengths at one time during soul possession and as such, control can be disrupted with a wavelength control technique (i.e Ultimate Move: Black☆Star Big Wave.