Mahou Tsukai no Yoru魔法使いの夜

Mahou Tsukai no Yoru (魔法使いの夜, Mahou Tsukai no Yoru? lit. A Magician's Night), officially subtitled as Witch on the Holy Night, is a novel written by Type-Moon co-founder Nasu Kinoko, initially released on July 28, 1996, though it isn't publicly available. It features Aozaki Aoko as the main character.

After the successes of his later visual novel works Tsukihime and Fate/stay night, Type-Moon announced that it was working on the story as its latest visual novel project, with further details of the project to be published in Type-Moon Ace. It was later announced that the visual novel. Release - 30.09.2010.

Source: Type Moon Wiki