Rasetsu (羅刹), Is an antagonist working for Fubuki in the anime Senran Kagura: Shinovi Master -Tokyo Yōma-hen-. She is a Sentient Yōma that served Fubuki's Mother and thus by extension, Fubuki. She is extremely loyal to Fubuki and Fubuki deeply cares for her. After Fubuki loses her parents, Rasetsu was the closest to family to her.
Rasetsu is a tall Yōma with a quite standard body for the series. She has a grey skin, covered with black feather-like parts, a lizard-like tail, pointy ears, seemingly orange eyes, white hair, and a horn and a third eye in the forehead.
Loyal, Rasetsu served Fubuki's mother until the latter got sealed away, and is protective towards Fubuki, for which she cares deeply, to the point of using all the strenght she can have when Asuka, Homura and Miyabi try to seal her.
Rasetsu served Fubuki's mother, who was said to be the most powerful Yōma the shinobies had ever seen. When Fubuki's mother was sealed away by her husband, Rasetsu saved Fubuki who got surrounded by shinobies that were theoretically ordered to protect her. Injured, Rasetsu met Kurokage, a renegade shinobi who guaranteed his neutrality, and leaves Fubuki to his cares, telling him that she will come back to get her again after she had finished healing. After over a year of living with Kurokage and Yumi, Rasetsu arrives to take Fubuki back.
During the events of Shinovi Master, she is found beneath the arena by the Crimson Squad and the Hebijo Academy that were attempting to sneakily free the Hanzo team, who were being held captive by Fubuki. To their surprise, Rasetsu reveals that she is intelligent and able to speak human language, before revealing herself to the rest of the cast up in the arena when Fubuki declares war on all shinobies. She follows Fubuki until the latter's fight with Kagura, and leads the Yōmas during their second invasion attempt, separated from Fubuki.
The fight at first is at her advantage, as her overall power defeats all the shinobies attacking her. When Asuka attempts to seal her forever, she resists and breaks the spell, unleashing all her power to become a giant, mindlessly raging Yoma as she had promised Fubuki she would use all her power to serve her. Ultimately, Asuka, Homura, and Miyabi all simultaneously perform the Seal in order to seal her away forever.
Rasetsu's story is different in Shinobi Master Senran Kagura: New Link, where she is eventually revealed to be the true main antagonist. Her goal with Fubuki was to eventually be able to get her old group of sentient Yōma back together, including Yasha and Shura.
Once Fubuki parts ways with her, she has to set out on her own. Her first target is to release Yasha from within Yūyaki.