Blood Blade

The Blood Blade is a sword that appears in Hanyō no Yashahime. It was first mentioned by Tōtōsai and confirmed by Jyūbei when questioning about the mark on Setsuna's right arm.

History
When Setsuna was under the control of her demonic blood, her elder twin sister attempted to absorb the excess demon power to try and calm her down. However, a red mark descended on Setsuna's right arm and some purple butterfly wings emerged from her back. Even for when Kin'u reapplied the seal on Setsuna's blood, the red mark didn't disappear.

The next day, Setsuna had her arm checked out by Jyūbei outside the Corpse Dealer's quarters.

Abilities and Techniques
The Blood blade resides in Setsuna's Right Arm and can extend be used to slash and infuse energy into blades such as Kanemitsu no Tomoe's blade.

Season One

 * "By the looks of it, this is a Blade Blood."
 * "A Blood Blade?"

Season 1

 * The Stolen Seal (first appearance; as a blood mark)
 * Episode 23 (Hanyō no Yashahime) (first indirect usage)
 * Episode 24 (Hanyō no Yashahime)

Season 2: The Second Act

 * TBA (first appearance and use as a sword)

Trivia

 * Much like that of Bakusaiga coming from Sesshōmaru's body in Episode 17 (FA), the Blood Blade came from inside of Setsuna's body.