Brain (ブレン Buren), or rather the Brain Roidmude (ブレンロイミュード Buren Roimyūdo), is responsible for collecting and managing information on the Roidmudes. Originally Roidmude 003 (Bat-Type), Brain copied the identity of the intelligence agency's programming deputy director Mitsuharu Kineta (杵田 光晴 Kineta Mitsuharu) while escaping into cyberspace to evade Proto Drive during the Global Freeze. He has a stoic and no-nonsense personality, and detests chaos. As such, he is irritated by the fact that all Advanced Roidmudes are those with brash, disorderly personalities, and he is in charge of reformatting the Roidmudes that Chase has captured. Brain sees Kamen Rider Drive as dangerous to their goals. He has the ability to inflict attacks on his target's nervous system, and can hack into nearby technology by tapping on his glasses. He despises any unruly behavior, even amongst his comrades, and is constantly irked by the idea that the unruly Roidmudes tend to be more powerful. Brain also serves as Heart's advisor but is wary of Medic's increasing influence on him, leading to Brain being overcome with envy for Medic, an envy that Freeze reveals to be Brain's emotional stimulant. Brain later assumes the alias of Sou Noumi (能見 壮 Nōmi Sō)[d] after siding with Freeze, presenting himself as a consultant from a Paranormal Science Institute sent to review the Special Investigations Division to trick Shinnosuke into attacking him so he would be suspended from the police force and as Kamen Rider Drive for attacking a human. After Freeze's demise, Brain decides to assume his Over-Evolved Form by using a Neo Viral Core to form a symbiosis with Nira to use the human's envy towards Eisuke Tomari as a booster agent. It takes all three Kamen Riders to defeat Brain, but his number survives. He is then subjected to torture by Medic, until he regains his old body back. He witnesses Banno's awakening as Gord Drive in horror, and apologizes to Heart for his previous indiscretions while warning him that Medic is under Banno's brainwashed control. Brain goes on the run to keep himself from being used by Banno in the second Global Freeze, and is ultimately placd under the Special Investigations Division's protection. Brain ultimately decides to help Heart save Medic by allowing himself to be captured, and he sacrifices his life to save her from being used to activate Sigma Circular.
Brain is portrayed by Shota Matsushima (松島 庄汰 Matsushima Shōta).