The plot will focus on Manaka Lala finding out about Saints' top idol journey, and will feature the return of many characters from across all the Pretty Rhythm series.
Source: PriPara Wikia
Houjou Sophy
Related works
Falulu is far away in the heart of the PriPara world in Puransu. The sparkle is disappearing from the idol sacred ground PriPara, and Falulu sends an SOS message to Laala and her friends. If the sparkle doesn't return, the PriPara world itself will disappear. Laala and her friends try to help Falulu, and they work together to save the PriPara world.
Source: ANN