"Show By Rock!!" is set in the vibrant world of Midi City, a bustling metropolis inhabited by anthropomorphic animals and mythical creatures. The narrative centers on Cyan, a shy and introverted cat girl who dreams of becoming a musician. One day, she is mysteriously transported into the world of Sound Realm, a parallel dimension where music holds immense power. There, she encounters the legendary band Plasmagica, whose members include the energetic pink alien Chuchu, the cool and composed wolf Retoree, and the mischievous ghost Moa. Recognizing Cyan's potential, the band invites her to join as their guitarist.

As Cyan adjusts to her new life, she discovers that music in Sound Realm is not just an art form but a force capable of combating dark entities known as Darklings, which threaten the harmony of the world. Plasmagica, alongside other bands like ShinganCrimsonZ and Criticrista, takes on the responsibility of protecting Sound Realm by using their music to purify these malevolent creatures. The series explores the challenges faced by the band as they navigate the competitive music industry, strengthen their bonds, and grow as musicians while fulfilling their duty to safeguard their world.

Throughout the series, Cyan's journey is marked by personal growth as she overcomes her insecurities and learns to embrace her passion for music. The dynamics between the band members are a focal point, with each character contributing their unique personality and skills to the group. The narrative also delves into the rivalries and alliances between different bands, adding depth to the world-building and highlighting the importance of collaboration and friendship in overcoming adversity. The story balances lighthearted moments with action-packed sequences, creating a blend of comedy, drama, and fantasy that appeals to a wide audience.