Summoned by Jester Karture as an Assassin in the fake Holy Grail War in Snowfield. She is a former candidate for the position of Hassan-i Sabbah, the pseudonym shared by the leaders of the League of Assassins, the Hashshashin. She was known a particularly faithful girl in a certain country whose existence is referred to as "merely a story." She underwent intense training to earn herself a name, and she was pious to the point in attempting to prove her faith that she was labelled as a "zealot" with despise by even those who worshiped the same God. While their group could be called a company of fanatics, her convictions were so beyond the norm that they earned her that title. She did not hate those who disparaged her because she believed the reason she was despised was because of her own immaturity and that her conviction was not firm.

She wished to become the sect's leader, which required that she acquire power that could be called Divine Miracles. These Miracles had some unique specifications in that they must all quickly and reliably snuff out the lives of heretics and infidels. The leaders in the past obtained their titles by achieving numerous miracles worthy of bearing the name of the Fallen Angel in the form of Zabaniya, so she continued her mad pursuit of self-improvement incessantly, seeking the miracles that were achieved by her predecessors. She recreated them one by one, but the World seemed to only shout "Still not enough" at her without pause. The other members were shocked by her achievements to the point where they could not believe what had happened. While she had achieved the miracles of all eighteen leaders in the past, no one in the sect acknowledged her right to inherit the leadership. It was her proof, soaked in blood and sweat, and she knew better than everyone what it really took to reach that point.

The faithfuls began to shun her, telling her that "What you achieved is no different from making copies of old tomes. You have not achieved your own Miracle, because there is still immaturity within you." While she did lack the ability to innovate, their denial was only half of the reason. They feared her, she who learned all of those techniques in the span of a few years. Their final reasoning was that "You are still too young. We cannot have someone like you bearing the title of our leader.", and although it was filled with nothing but excuses, she obeyed without question. She simply questioned her own faith, and believed herself to be juvenile in having defiled the secret techniques of their past leaders. She did not blame anyone, but still continued the quest for her own secret technique.

"The Hundred-Faced One," a man capable of resolving every single situation masterfully, eventually became the nineteenth leader, and upon recognizing his ability, Zabaniya: Delusional Illusion, was one she did not have, she was ashamed of her own immaturity rather than filled with envy. She did not fulfill anything in the end, nor did she receive any acknowledgement. She merely lived as a zealot, and she was not even allowed to be martyred for her faith. She spent her life meaninglessly until the end, but still bore the World no hatred. Still ashamed of her immaturity, she again dove into the whirlpool of faith because she has no emotions to allow her to bear a grudge. The only things she despised were the false idols of infidels, making her a zealot that no normal man could redeem. That is her whole story which merely disappeared into the abyss of history as that of another zealot, and while it should have ended there, it was reborn the instant when the zealot become the False Grail's chosen.

(Source: Type-Moon Wikia)