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Mu, literally meaning "Nothingness", is the main antagonistic faction in Kamen Rider Drive Saga: Kamen Rider Brain web series.
"Mu" is an evil organization only appearing in Brain Roidmude's dream world, formed during Brain's data reconstruction by Go Shijima during his continuous quest for reviving Chase (as it revealed in Part 2 of Brain Saga). Mu were composed by of past adversaries of the Kamen Riders and were a comical parody to Shocker.
Targeting subjects with an IQ point of 600, the agents of Mu captured Brain for their experiments, much to Brain's chagrin. As the Leader of Mu (the dream world version of the Great Leader of Shocker) prepares to erase Brain's memories, a blackout happened and Brain himself was saved by Crystal Peppler (the dream world version of Krim Steinbelt/Mr. Belt), with the former experiencing Deja Vu after seeing Peppler.
With Peppler's help, Brain was out of danger and later uncovered a Driver, tied in his handkerchief out of the blue. As Mu prepare to execute Peppler for his betrayal, Brain transformed into his Super Evolved Roidmude form to fight them. However, he failed. As he fell to his apparent death, Brain miraculously revived once more and transformed into Kamen Rider Brain. After transform, Brain defeated every Mu members except the Leader, before escaping with Peppler on his motorcycle.
- Leader of Mu (leader)
- Kamen Rider Dark Kiva
- Kamen Rider Wiseman
- Kamen Rider Poseidon
- Kamen Rider Duke
- Kamen Rider Dark Ghost
- Kamen Rider Another Para-DX
- Crystal Peppler (defected)
- Mu acts as a full parody to Shocker but is more comical in every ways.
- In addition to the organization's parallels to Shocker, both the Leader of Mu and his subordinate Oogumo Great Leader are voiced by veteran voice actor Tomokazu Seki, who has served as the voice of the Great Leader of Shocker and his incarnations following the death of Goro Naya. Pratically, the Leader of Mu is a direct parody to the Great Leader.
- Mu's intention of creating Riders with someone with 600 points of IQ is a direct reference to Takeshi Hongo/Kamen Rider 1, who had an IQ point of 600 and became the first Kamen Rider after being experimented by Shocker agents.
- While the flag of Mu uses the corresponding kanji character (無), its leader speaks through a unique insignia which is a stylized form of the katakana counterpart (ム).