In the Battle Angel Alita universe, the possession of a brain (脳 nō?) is a key determinant of what it means to still be considered human given the high degree of cyberization that has taken place. This distinguishes a person from other sentient beings that do not have brains, such as androids and robots. Brains play a significant role and function in Battle Angel Alita, which was greatly expanded in Last Order.
Battle Angel AlitaEdit
After Daisuke Ido found Alita in the Tiphares dump heap, he discovered that her brain was still intact, having fallen into a state of hibernation despite her apparent age (200-300 years). Throughout the manga and later in Last Order Alita's lost memories slowly begin to return, usually after she is "shocked" into recalling them through certain events or circumstances that are similar to those that she faced in her past.
When Alita went to register as a hunter-warrior, her hunter ID was electronically stamped on her neuroglia, which was explained as the only available means of identifying a cyborg, as they have no natural cell patterns. Conversely, to collect the reward money for bringing in a bounty, the hunter-warrior needs to bring their head to a Factory for identification and confirmation of brain death. Under Factory Law, causing brain death, brain injury, or trading live brains are Class B offenses.
Shortly after Alita registered, Izuchi tried to procure a dog's brains for Makaku to feed his endorphin addiction. When his attempt was rebuffed by an unnamed Scrapyard resident, Makaku went berserk and began to grab random bystanders, cracking their skulls open to suck out their brains. Later that night he was in the process of feeding on someone when Alita ran into him. Because of the loss of his eye during their fight, he attempted to crack Alita's skull open to get to her brain, but was thwarted by Ido. After revealing his true form, Makaku threatened to consume Ido and Alita's brains before fleeing.
With the Power Body, Makaku used it to stomp on several hunter-warriors who were thrown out of Bar Kansas during the brawl with Alita and sever their heads. When he burst into the bar, he killed Reptile by slicing him with the grind cutters in his hand, exposing the latter's brain and catching it with his tongue. Following Alita's pursuit of Makaku into the sewers, Ido speculated that her Berserker Body had the ability to defeat Makaku if she could activate its survival mode, which was connected to her cerebral cortex. During the fight Alita unlocked the Berserker Body's ability to generate plasma, which proved instrumental in defeating Makaku. She also learned how he had nearly died and his brain had been transplanted into his Maggot Body.
During Alita's pursuit of Megil, the latter injected the lycanthropazine directly into his brain to transform into his monster werewolf form. Alita later killed Megil with a blow to the head that caused his brains to spill out of his ears. When he was confronted by Hugo and Alita, Vector revealed that he could send the former to Tiphares, but only in the form of his organs, as he sent an individual's worth to the floating city every month. This included a brain in a preservation canister.
During Jashugan's Top League challenge race, he suffered a spasmatic attack and was forced to pit. His medical team was unable to revive him after his brain functions ceased and it took Ido's intervention in the form of sending Shumira's brain waves through an amplifier to Jashugan to bring him back.