Kouta and Mitsuzane attempt to warn the Beat Riders about Yggdrasill's manipulation, only to find that Yggdrasill is deploying Kurokage Troopers to silence anyone who knows the truth as Zangetsu uses a new belt model. Meanwhile, Mai encounters the mysterious girl who resembles her.

A mysterious bacteria is infecting people in Zawame City. In the crisis situation, Kouta, Mai, and Mitsuzane try to find out the cause behind this.