A Shibito Brain is a specific type of shibito who is helping control the mutated/evolved shibito. If the Brain is knocked out, so are the specific shibito associated with them.
Forbidden Siren[]
They appear after the shibito bathe in the mana river during day 1 (at 12:00); the first shibito brains are seen by Tamon Takeuchi at 20:41. Then by Naoko Mihama (22:11) and Risa Onda (22:52).
Later during day 3; Risa Onda is also seen as a brain shibito (at 16:00) as well as Reiko Takato in the nest (aprox. at 22:13).
Siren: Blood Course