Also known as: Oktavia_von_Seckendorff, オクタヴィア・フォン・ゼッケンドルフ, 人魚の魔女
Mahou Shoujo Madoka Magica character.
An armored mermaid Witch (Madoka Magica) introduced in episode 9 and seen again in episode 10. Her minions are Holger (Madoka Magica) (the performer) and Klarissa (Madoka Magica) (the backup dancer).
Note: Major spoiler warning!
She is the result of Miki Sayaka becoming a Witch. Also becomes a Stand (Jojo)-like entity for Sayaka in Mahou Shoujo Madoka Magica: Hangyaku No Monogatari.