|Grateful Rock Festival|
|English||Grateful Rock Festival|
|Japanese Air Date||June 14, 2015|
|Opening||Youth is Non-Stop!|
|Ending||Have a Nice Music!|
|← Episode 10 - Reserve Rhapsody||Episode 12 - Our Youth is Non-Stop! →|
Grateful Rock Festival (グレイトフル・ロック・フェス Gureitofuru Rokku Fesu?) is the 11th episode of the series. It was released on June 14, 2015.
As everyone assembles at Boodookan for the Grateful Rock Festival, Cyan grows concerned that she hasn't heard from Strawberry Heart since rescuing Chuchu, while Dagger prepares to use a song written by Grateful King to take over Midi City. Midway through the festival, Plasmagica, Shingancrimsonz, Tsurezurenaru, and Trichronika are attacked by a Dark Monster, capturing everyone except for Cyan, Shu-zo, and Darudayu. As Darudayu fights against the monster, Cyan discovers that the Dark Monster is actually Criticrista's Rosia.
- This was the first episode in which 4 Bands was in the dark monster zone at the same time.
- Rosia was the dark monster.