Kinoko Nasu's original plans for Fate/Stay Night, featuring a girl with glasses as the protagonist and a male Saber, have been adapted and expanded in what's been named Fate/Prototype. Hikaru Sakurai has been working on a series of prequel light novels called Fate/Prototype: Fragments of Blue and Silver, and while this is on break between its third and fourth parts, she has launched a spin-off titled Fate/Labyrinth in April 10th's new issue of Comptiq magazine.
In three-part Fate/Labyrinth, Manaka Sajyou, prototype for Illyasviel von Einzbern, older sister of Prototype's heroine, and former master of the male Saber enters the alternate world where she possesses the body of a master who has summoned an (apparently) familiar female Saber. There she must participate in a variant Holy Grail War where four servant/master pairs race to the bottom of a labyrinth.
明日（4月10日）発売のコンプティークにて、新スピンオフ『Fate/Labyrinth』集中連載第1回が掲載されます。──迷宮。少女。亜種聖杯。そして、蒼銀を纏う騎士王がひとり。 pic.twitter.com/4JL3q98ShU— 桜井光 (@h_sakura) April 9, 2015