"GS Wonderland" is about the 1960's Group Sounds bands - A Japanese pop movement inspired by the Beatles and other mid-1960's Brit Pop. Three young men set out to start their own band "The Diamonds" when they are signed to a recording contract during their very first rehearsal. Things turn for the unexpected when their agent brings Mick (Chiaki Kuriyama) into the group as their keyboardist.

• Chiaki Kuriyama
• Takuya Ishida
• Hiro Mizushima
• Yōsuke Asari
• Shinji Takeda
• Sousuke Takaoka
• Mana Mikura
• Kendo Kobayashi