A collaboration event between “The Idolmaster SideM” and Seibuen Amusement Park, titled “Super!! Retro Rose Party,” will be held from October 30 to December 1, 2026. Idols from 315 Production, dressed in Showa-era retro costumes, will make an appearance alongside autumn roses. On October 31, November 1, and November 22, the “Super!! Retro Rose ‘Special’ Party” will be held, featuring appearances by the cast, and a joint stamp rally with Tokyo Joypolis will also take place.