Falulu is a mysterious vocal doll who appears in episode 1 and later makes her debut as an idol in episode 17.
At the beginning of the series, she is very naive and doesn't know a lot of words so she tends to repeat the words and actions of others (even copies Laala's and Mirei's catchphrases and actions). Her voice sounds slightly robotic, and she tends to call certain things (like the Prism Voice and Laala) sparkling.
Despite not knowing what emotions are, she still expresses anger, fear and happiness. She is also very smart, being able to solve long equation problems within seconds.
Episode 37 spoilers
After her re-awakening in Episode 37, Falulu's personality becomes much more human-like and vivacious and her speaking voice, as well as her singing voice, loses its robotic quality.
She also became more responsible and worrisome since she now has 100 little sisters to watch over.
(Source: Pripara Wiki)