Anzen Mamajo

"She was indeed my Ultimate Demon. She was indeed by greatest success. And was indeed, out of everyone else, absolute. But...I did one mistake...I gave her a "will"."

- Azazel talking about Anzen Anzen Mamajo (暗然魔魔女, Dark Demon Witch) is a Human Maken, created by Azazel, and is his greatest creation to date. She was branded the title Experiment No. 1000: Echidna (試作号千:エキドナ, Shisaku Gō Sen: Ekidona lit. Prototype Model One-Thousand: She-Viper), and as the 1000th experiment to be tested out, she was granted the accumulated knowledge and skill of the last 999 experiments prior to her, granting her power greater than before, but also destroying her former body, until she recreated a new one, molded and stabilized out of Black Blood, making her a unique case as a Human Maken.

Anzen is the only known creation to gain the title Ultimate Demon (究極魔, Kyūkyoku Ma lit. Final Devil), Azazel's ultimate goal, and thus, would make her his most powerful. However, due to the accumulated knowledge of 999 humans before her, she developed her own will that couldn't be controlled, and as such, managed to escape, later became known as Black Witch (黒魔女, Kuro Majo), due to her distinctive look and Black Blood mastery.

Trivia

 * Anzen's appearance is based off of Marina Arusu from Date-a-Live: Ars Install.
 * In Greek Mythology, Echidna is known as the "Mother of all Monsters", being known to have mothered several infamous monsters in Greek legend.