The Psi Reavers' brain structures are located in the side niches of the Brain Chamber (the Greater Psi Reaver's brain stem is located in the middle recess on the left side). There is also a unique, powerful Greater Psi Reaver floating above. The Brain Chamber and its entrance are guarded by numerous Rumblers and Psi Reavers. The Projections (previously unseen in the cutscene) orbit around the organ and protect it, lighting up when the Brain is attacked. The Brain itself does not attack, but is almost invulnerable until its three Psionic Defensive Projections (also called Brain Defense Nodes) are destroyed. Even when angered, they leave the aggression to their minions. The Many are cordial and measured in their communication, never insulting soldier directly. Most likely the Many perceive their actions as being in the interest of what they consider the greater good. They hate chaos and discord, yet they incited much death and suffering directly. The Many display some hypocrisy: they rail against cybernetics and machinery, yet it was them who instructed Marc Miller how to create the Midwives.

The Many are not above using violence to ensure the success of their goal - aside from the invasive conversion process that turns humans into shambling Hybrids, they are also responsible for most of the atrocities aboard the Von Braun, including the creation of the Cyborg Midwives. They also believe that they must bring an end to the human discord by absorbing all life. The Many view individuality as a weakness and a source of conflict. The Brain also possesses great Psionic power, which it uses to both protect itself and communicate directly with the player. It displays a degree of intelligence and is aware of player's actions throughout the game, thanks to the psychic link with the Annelids. The Brain is most likely the cognitive center of the Many, however the specifics of its functions are unknown and unexplained.

Soldier first sees the Brain in a hallucinatory sequence on the Engineering Deck, and finally fights it in the Body of the Many.

The Brain of the Many is its central mind and the first boss in System Shock 2.

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