|“||Are you really sure you're willing to set free a monster even worse than Lucy?||”|
Isobe was Kurama´s personal assistant. His biography and personality are completely different between the manga and the anime, with him playing a much more complex role in the manga. While it is never stated directly, it seems likely he gained his position when Kurama's original assistant, Oomori left the Diclonius Research Institute after the euthanizing of his infant daughter, who was a Diclonius.
Working as a personal assistant to Kurama, this character is rarely addressed by name, but appears in and effects events in many chapters of the manga series, nearly from the start. Along with Shirakawa, his most prominent appearance occurs when he is given charge over Mariko's mission to hunt down Lucy, when Kurama abruptly leaves and Saito is savagely killed by Mariko. After Saito's death, Isobe develops a low opinion of her, feeling that she manipulated Mariko's emotions regarding her parents' love for her. He is also present when Mariko and Nana argue about Kurama without realizing each is talking about the same man. A morally-conflicted man, he feels that implanting the bombs in Mariko's body is inexcusable, but stands ready with the remote control to either temporarily delay the bombs' detonation or selectively blow them up at will. Slicing away the arm that held the remote, Mariko emotionally manipulates him into giving her the anti-detonation codes, and then taunts him before finally beheading him. It can be speculated that knowledge of the fate of his predecessor Oomori and sympathy for his plight made him more open to Mariko's trickery.
In the anime, Isobe is a colder, more clinical, and less complex character, reflecting more of his scientist role. He also looks different than his manga incarnation, as he sports glasses and a mole near his lower left jaw. He appears to have no problem using or controlling Mariko, though he is shocked by the method chosen to control her, and also shows no concern about Shirakawa's well-being when she could have been killed by stray gunfire as SAT soldiers tried to kill Lucy and Kouta. During the final episode, he watches Mariko and Lucy fight, saying it's better "to let the monsters fight amongst themselves." This comment could be directed either toward both Lucy and Mariko being the strongest of their kind or directed at Diclonii in general. He also watches as Mariko and Kurama die together, as he has the cell phone that serves as the remote for Mariko's bombs. After their deaths, he is prepared to execute Nana despite knowing how much his late boss loved her. While aiming a gun at Nana, he remarks on the reward he would get for putting her down, but he is decapitated by Lucy before he can do more than talk.
At the end of the second episode, Kurama and Shirakawa observe Nana before choosing to send her to retrieve or kill Lucy. A scientist assists them, and based on his role as supervisor of Nana, his voice (in the English version, at least), and appearance, this man may or may not be Isobe. Whoever this character is, he has the odd distinction of being dubbed in Japanese, but somehow his lines were skipped for the dubbing process.