Fate/Prototype: Sougin no Fragments

Prequel to Fate/Prototype.

Tokyo, 1991. Seven mages gather to summon seven heroes from history, myth, and legend to do battle in a great ritual. The last ones standing will obtain the Holy Grail—a font of limitless power said to be able to grant any wish. One such Master is Manaka Sajou, a young maiden with immense expectations placed on her. But when she lays eyes on the one she summons, what she sees is not her Servant but the fairy tale prince of her dreams!

(Source: Yen Press)