Light novel The Familiar of Zero (ゼロの使い魔) had got 20 volumes and four seasons of TV anime before the late author Noboru Yamaguchi (山口昇) even finished the ending. The publisher later released two more books together with an unnamed author. In the special volume The Familiar of Zero: Memorial BOOK, the mysterious figure is revealed to be light novel Bladedance of Elementalers’ (精霊使いの剣舞) writer Yu Shimizu (志瑞 祐).
In 2015, the publisher said they would be finishing The Familiar of Zero with a ghostwriter. The identity of the writer remained unknown even after four months of the final book’s release. In Memorial BOOK, Yu Shimizu revealed his identity in the author’s remark chapter.
He also mentioned Yamaguchi’s plan for sequel chapters about the child/children of Saito and Louise. Yet, he wishes to write about the couple’s daily life if he is given the opportunity to carry on being the ghostwriter for the series .