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Do not proceed unless you want to be spoiled.
Kira☆Pika (きら☆ぴか?) was an idol group in the Kirarin Revolution anime series. The group consists of two members: Tsukishima Kirari and Mizuki Hikaru. Kira☆Pika was a Hello! Project unit consisting of the two character's seiyuus, Koharu Kusumi from Morning Musume and Mai Hagiwara from °C-ute.
All of Kira☆Pika's songs can be found here.
By the last episode of the anime, Kira☆Pika was long split up, but Hikaru shows up to Kirari's performance of "Happy☆Happy Sunday!" and is seen smiling. They most likely remained best friends since they split.