Mahoutsukai no Yoru

Nasu wrote the original script for Mahoutsukai no Yoru in the winter of 1996, and only showed it to a few close friends before moving on to other projects after the novel was rejected by several competitions due to it being over the page limit. Mahoutsukai no Yoru was Nasu's first novel, and marks the beginning of Nasu's fictional worldview.

In early 2008, a game version of Mahoutsukai no Yoru was announced along with Girls' Work and a Tsukihime remake in the first issue of TYPE-MOON Ace. TYPE-MOON chose to take a different direction for the new game, unlike Tsukihime and Fate/stay night, Mahoutsukai no Yoru is an all-age game with the lead artist being Koyama Hirokazu. Nasu mentioned in an interview in 2008 that he wanted the game to be a "visual story" rather than a "visual novel game." Later announcements revealed that the game will not have voice actors or branching story routes.

The game was set to release sometime in 2009. After several delays, the game received a September 2010 release date. In September, however, TYPE-MOON pushed back the release date to 2010 winter, and later TBA 2011. A demo of the game was released with TYPE-MOON Ace issue 7, along with a confirmed release date of April 12, 2012. The 1st edition of the game also included an artbook titled Mahoutsukai no Kiso Onritsu.