The Fate/kaleid liner PRISMA ILLYA Twitter page has revealed the title of the series’ upcoming movie to be Fate/kaleid liner Prisma☆Illya: Licht – Namae no Nai Shōjo, or Fate/kaleid liner Prisma☆Illya: Licht – Nameless Girl (note that this is not an official translation). A key visual was also released.
Plot details for Fate/kaleid liner Prisma☆Illya: Licht – Namae no Nai Shōjo have yet to be revealed, but the presence of Julian and Erika Ainsworth in the key visual suggests that it will continue where 2016’s Fate/kaleid liner Prisma Illya 3rei! left off.
Fate/kaleid liner PRISMA ILLYA, a magical girl spin-off of the Fate series, started as a manga by Hiroshi Hiroyama in 2007. It was adapted into an anime series in 2013, which spawned several sequels and the 2017 prequel movie Fate/kaleid liner Prisma Illya Movie: Oath Under Snow.
Crunchyroll describes the first season as:
Illya (Illyasviel von Einzbern) is a typical young girl attending Homurabara Academy who just happens to have a slight crush on her brother-in-law. Then, one night, a magic wand called Magical Ruby falls from the sky into her bath and tricks her into signing a contract…
