The wait for Prisma Illya Season 5 continues even as a continuation of the anime series had been confirmed. Titled Fate/kaleid liner Prisma Illya: Prisma Phantasm, the new anime will be an OVA episode that will screen in Japanese theaters in 2019 before being released on Blu-Ray and DVD.
In the fall of 2017, voice actress Mai Kadowaki, who plays the titular character Illyasviel von Einzbern in the anime TV show, announced the new Prisma Illya anime project by saying, “In addition, a surprise from [Shirou Emiya voice actor Noriaki] Sugiyama is the big secret announcement about the production decision for a sequel.”
Based on the vagueness of the announcement, some believed at the time it was possible the voice actress was talking about Fate/kaleid Season 5, but it turns out the new project was simply an OVA episode.
While not a full new season, the Prisma Illya OVA episode will apparently be a sequel to the 2017 movie Fate/kaleid Liner Prisma Illya: Sekka no Chikai (or Fate/kaleid Liner Prisma Illya: Oath In The Snow).
— プリズマ☆イリヤ公式アカウント (@prisma_illya) February 28, 2019
However, it’s possible that a true Prisma Illya Season 5 will eventually be announced in the future since the entire manga series has not yet been adapted.
Season 1 adapted the first manga series while seasons 2 and 3, 2wei! and 2wei Herz!, covered the events of the manga series with the same name. Season 4 was based on the third manga series, 3rei!, and the Oath In The Snow movie adapted the flashback scenes from Chapters 31 through 43 of the 3rei! manga.
Unfortunately, there is currently not enough new content yet for the fifth season. The 3rei! manga is currently up to Volume 10 and 18 new chapters have been released that cover story events beyond the movie.
Therefore, it may take until 2021 or beyond until there are enough new chapters available for producing Season 5. But at least anime fans can find solace in watching Fate/kaleid liner Prisma Illya: Prisma Phantasm in 2019!