|Japanese Voice||Ryouko Tanaka|
|English Voice||Jamie Marchi|
Nei Isayama (諫山 冥) is a major antagonist in the Ga-Rei: Zero.
Mei is the older cousin of Yomi Isayama. Despite initially trying to hide it, Mei always hates Yomi ever since Yomi was adopted into the Isayama family.
She desired control over the family's power sword, and the animal spirit warrior linked to it, but at first did not oppose her uncle Nakaru's plan to give the role to Yomi, knowing that Yomi was the better fighter out of the two, but that Yomi would probably die anyway early on due to the recent massive surge in supernatural activity.
Kazuhiro Mitogawa who was causing these surges then appeared to Mei along with his swarm of butterflies and revealed himself to her as the true source of all of this darkness and all of the deaths that resulted. He claimed to her that they were attracted to the stone in his eye, and then tried to kill her, with the two duelling with swords until she impaled him in the stomach. Kazuhiro laughed at this, as in spite of the sword’s mystic abilities it had no effect on him, and he touched Mei’s hand, which caused him to see inside Mei’s mind and see how cruel and manipulative she was as a person.
He told Mei that he liked her for how dark and similar to himself she was, only for him to then stab her in the chest with a lance he produces using his powers. Hours later, one of his butterflies was seen feeding off of the blood from Mei’s corpse, when she suddenly and mysteriously rose from the dead. It is later revealed that half of the dark spirit energy that followed Kazuhiro around was now associating with Mei (i.e. he transferred some of his powers to her), in order to spread destruction throughout the city.
Mei, now mentally corrupted by Kazuhiro, then proceeded to murder her uncle Naruku before he could declare her adoptive cousin Yomi as head of the family and wielder of the spirit beast, in order to take that honour for herself. Mei then completely displaced Yomi and was declared head of the family, taunting and humiliating Yomi, and demanding their family’s powered sword from her.
Upon receiving the sword, Mei suddenly remembered her encounter with Kazuhiro, and his butterflies appeared and surrounded her and pursued her out of her home. In the streets, running from his butterflies, Kazuhiro confronted Mei and told her about how useful her anger and hate can be as weapons, and he used his magic to non-fatally tear open Mei’s chest to reveal that he had placed one of his magic stones within her when he impaled her, and told her that everything was working to her advantage. He smiled gleefully while Mei screamed in agony and in horror at everything she had done (which she was only just starting to remember, as her true personality was temporarily returning while the stone was exposed).
Later that day, in a clearing, Mei attacked Yomi using the spirit beast linked to her powered sword, in an attempt to kill her. In the attack, Yum cut off Mei’s arm, but it grew back due to the stone's power.
As their duel became more and more violent, Mei began monologuing about how easy it was to kill Yomi’s adopted father, causing Yomi to stab her repeatedly, causing no damage until she hit the Kazuhiro’s stone within Mei’s chest, which caused her healed wounds to suddenly re-open, and her original personality to be restored.
Having become herself again, Mei lost all memory of everything she did under Kazuhiro’s influence, and was confused and terrified when Yumi continued attacking her. She pleaded for her life to Yomi, not knowing what to say, but her cries fell on deaf ears, as Yomi pinned her to the ground and decapitated her.
After Mei's death, Kazuhiro's butterflies attacked Yomi in blade form, and seriously injured her, as well as taking away her ability to speak. Yomi was also considered the prime suspect in Mei's murder, and it was misinterpreted that she had killed Mei just to grab control of the family for herself.