A promotional video has been released Kadokawa today in regards to the upcoming Fate/kaleid liner Prisma Illya 3rei anime series. The fourth anime season of the Fate/kaleid liner Prisma Illya series will be releasing this upcoming summer. The series is based off of a original manga which first released September 26th 2007 and ended November 26 2008 with 2 volumes released for it, sequels later released which would all get anime adaptions. The first anime aired on June 22nd 2013 and ended September 7th 2013 releasing 10 episdoes. A sequel under the same title as the manga Fate/kaleid liner Prisma Illya 2wei would later get released between the dates of July 10th 2014 and September 11th 2014 with 10 episodes releasing for it. The third and most recent season titled Fate/kaleid liner Prisma Illya 2wei Herz started on July 25th 2015 and ended today September 26th 2015 with 10 episodes releasing for it.
Now below is a plot summary for the upcoming new series provided by MAL:
Spin-off of Fate/stay night with Illyasviel von Einzbern as the protagonist, living an alternate life as a school girl. While taking a bath, she stumbles upon Kaleido Stick Ruby, who turns her into a magical girl.