He is an artificial intelligence created by Eisuke Harukawa from a copy of his brainwaves. Created to help Harukawa with his project to recreate the brain of a person from zero. However, seeing Harukawa's methods and intelligence as far inferior, he took it upon himself to go to much greater lengths to continue the project. While almost invincible in the digital world, the Electronic (Denshi) Drug was used by HAL to brainwash people into protecting the supercomputers that maintained his system. His mystery was the equivalent to a banquet to Neuro and upon eating it, Neuro was filled with energy, more than enough to recover from past wounds.
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