The third season in the Fate/Kaleid liner Prisma Illya series, following from where the second season, Fate/Kaleid liner Prisma Illya 2wei finished.

Following the second season, Illya and friends have successfully captured all seven Class Cards. However, there is still an anomaly left on the city's ley lines. They are tasked to investigate what is causing it and finds the possibility of an eight Class Card. This time, summer break has started and Illya has a lot of fun activities with Miyu, Kuro, and her schoolmates. Soon, they are caught up with Rin and Luvia's plan to find and capture the most dangerous Class Card of all.—heyitsnuel