Merm4id and RONDO take center stage in the special episode of D4DJ, known as Double Mix. The plot revolves around the legendary DJ festival, "D4 FES," and Merm4id's dream to participate in it. The female trio - Marika Mizushima, Saori Hidaka, and Dalia Matsuyama - become worried about Rika Seto's peculiar behavior during a swimsuit photoshoot. Meanwhile, Tsubaki Aoyagi from RONDO spends time lost in thought at the chapel, contemplating how their world can grow. Following their live performance at the ALTER-EGO clubhouse, Rika interrupts Tsubaki's private moment with Nagisa Tsukimiyama, Hiiro Yano, and Aoi Miyake. Rika, who heavily relies on luck and charm to live her life, astonishes everyone with an unexpected proposition.