The Brain Trust is a secret organization found in the manga/anime series GetBackers.
In the anime, the God of Infinity Fortress was revealed to be a secret cabal known as the "Brain Trust," a group of powerful individuals – scientists, engineers, artists, politicians, patrons, and super-natural beings - that created the Infinity Fortress as an experimental site where any infinite number of ideas that could be conceived could be tested. Gensui Radou had been a member of the Brain Trust before discovering their true intent and leaving in disgust. Likewise, Masaki Kurusu was a Brain Trust operative who had been installed in Lower Town as a member of the VOLTS in order to observe their actions.
Continuing his plan to free Lower Town from the “God’s” control, MakubeX tapped into the “Archive,” the massive computer bank that controlled the virtual reality of the Infinity Fortress, and schemed to transfer the data that shaped Lower Town into his own computer system, thereby removing it from the God’s control. Aware of this plan, the Brain Trust ordered Kurusu to return to the fortress and abduct MakubeX in order to stop him. The news of his abduction reached the GetBackers, however, who defeated Kurusu and put their own plan into motion – with the help of Gensui Radou, they transferred Lower Town’s data into the computer banks of their associate, Paul Wan, and Ginji proceeded to destroy the Archive. With the Brain Trust’s copy of Lower Town’s data destroyed, it was finally freed from its control, fulfilling MakubeX’s desire.
In the manga, the Brain Trust is akin to its counterpart in the anime - a secret cabal formed by the best scientists, engineers, artists, politicians, patrons, and super-natural beings. Various characters were revealed to be members: Ban's grandmother was the head of the department which oversaw matters of the occult, while Kagami was a physicist. However, the manga provided much more of a twist: The members of Brain Trust, and Brain Trust itself, actually originate from a separate plane of existence. It is not just Infinity Fortress that is a virtual reality, but all of the world of GetBackers. In fact, the world of GetBackers was essentially a "backup copy" that Brain Trust, existing in the "real world", had hoped to create using the Archive as a template of the world. It was through Kagami Kyoji's scientific theory, known as the "Mirror Effect", that the world of GetBackers were able to take actual form on a separate plane of existence. A great number of characters in this second world, in fact, exist in the real world, except with exaggerated qualities. Fuuchouin Kazuki, in the real world, is actually a girl, being a musician of Japanese traditional music, and girlfriend to Kakei Jubei, who is a young professor at acupuncture teaching at a prominent university in Tokyo. Akabane Kurudo himself is actually a surgeon. Amano Ginji himself is actually the virtual representation of the son of the head of Brain Trust, Ginji's "mother"; the "real" Ginji had actually died at a young age, and Ginji's "mother" created the Amano Ginji in the second world as an avatar of what the "real" Ginji might've grown up to become, providing him with the alter ego of Raitei to protect him. Brain Trust, however, soon realized that, after much research, that willpower seemed to be the actual driving force behind humans, a huge factor behind the strife in the world that prompted the formation of Brain Trust and their goal to synchronize all human thought to save the human race from decadence and eventual collapse.
However, Brain Trust soon realized that their "virtual world" was going rampant, diverging off actual reality, creating new rules of physics and phenomenons that would otherwise be impossible in the real world; this might explain why the characters of GetBackers are gifted with superhuman abilities, and why pseudoscience is prominent in their world. They soon realized that their efforts were sabotaged by the Witch Queen, Ban's grandmother, who led a small group of traitors against Brain Trust. With little options left open to them, Brain Trust decided to "reformat" their virtual world, which they deemed too corrupted and damaged to be salvaged, a full "restart". To achieve this end, Brain Trust ordered the Archive to begin the reformatting of the virtual world, all while selecting a single person within that virtual world with the proper willpower and strength to ascend to Babylon City and assist in steering that world back it the right path with his willpower.
At the end of the manga, this person turned out to be Amano Ginji, and his "mother" revealed the actual nature of Brain Trust to him. However, Ginji stated that, despite their world, compared to the "real world", was far more violent and dangerous, he did not believe that "happiness" came through "peace", comparing Ura Shinjuku in his world with the "real" Shinjuku that the Akabane Kurudo of the "real world" showed Ginji prior to Ginji's meeting with his mother. Ginji desired for a world that he was familiar with, a world that had bonds with the people he knew. Although Ginji's world is not what Ginji's mother considered to be "her ideal world", she ceded to Ginji's desire for his world, admitting to herself that, with Ginji's willpower, things were likely to turn out to be for the best. With Ginji's wish fulfilled, Ginji himself returned to his world to the company of his friends as the reformatting undid itself, saving everyone that had been doomed to the battle of Babylon City.