Monad is the Proxy of Mosk. She is voiced by Sachiko Kojima in the Japanese version, and Carrie Savage in the English. She is the Proxy of Birth - hence, she is the counterbalance to Ergo Proxy, the Proxy of Death. Similarly, Kazkis is the Proxy of the Sun and Senex, his partner, is the Proxy of the Moon.
Said to have loved Ergo, Monad is the Proxy and creator of the Mosk dome. Monad and Proxy One made an agreement to remove Ergo Proxy's memories so he could abandon his Proxy duty of death and become human. Monad, because she loved Ergo Proxy, sacrificed herself in the process of removing Ergo's memories and creating the Vincent Law alter ego - putting her into a coma and destroying her mind. In her comatose condition, she was no longer able to protect the Mosk dome when Donov Mayer, head of the Romdeau dome, bombed Mosk into oblivion in retaliation for his beloved Proxy One abandoning them to go to Mosk. Vincent Law, Ergo Proxy's alter ego, survives the bombings and is ushered back to Romdeau as an immigrant (unbeknownst to anyone in Romdeau except Proxy One). Flashbacks when Re-L finds the Mosk Dome proxy seat shows Monad sitting on her 'throne' as the bullets of the Romdeau invaders fly past her.
Monad's body was retrieved from Mosk, and brought back to Romdeau to replace the missing Proxy One. Daedalus reports that he was given charge of Monad Proxy when he was given the job of the Chief of the Health and Welfare Bureau; having the job of making sure that Monad remained unconscious and comatose.
Daedalus reported that Romdeau scientists were not able to identify a physical gender of the Monad Proxy. The Pulse of the Awakening woke her up and she escaped from the Health and Welfare Bureau in an instinctive need to reunite with her beloved Ergo Proxy, causing the deaths of forty-two of Romdeau's citizens in one night. Monad was drawn to Vincent Law and killed by Ergo between Confessions of a Fellow Citizen and Leap Into The Void.
Monad's corpse is found by Re-l Mayer as she follows the Escape Route that she finds in Vincent's apartment. She takes Daedalus to the corpse, and he is shocked because Monad is supposed to be immortal. He hides the Proxy and tries to siphon off energy from the Dome to revive her, but to no avail. It is revealed later that Monad is either Daedalus's raison d'être or part thereof. When Daedalus is disciplined by Romdeau and stripped of his status as Head of the Welfare Bureau, Monad is consficated from him. He later regains possession of Monad through making a deal with Raul Creed. Monad Proxy's body was used by Daedalus to create the FP-shells used to kill a Proxy. When Daedalus feels that he has been abandoned by Re-L Mayer, he makes a true clone of Monad that includes the Amrita cells (he grew the cells himself to create the second clone) that is growth-accelerated and has Re-l's face, but with Monad Proxy's powers. This is "Real" Mayer, who, in addition to Monad's powers, gains Monad's love for Ergo Proxy or Vincent Law. Real Mayer has all of Monad's memories.
Monad is Proxy XIII, as evidenced by the numerical mark on her personal proxy pendant, which ended up in Vincent Law's hands. Monad's corpse suggests that her nightmarish appearance is the result of surgical tampering by Romdeau's scientists. It is unknown what she looked like prior to their experiments.
The Real-Monad's fate mirrors that of Icarus in Greek mythology. The progeny of Daedalus, Monad uses her newly gained wings to ascend into the sky. Daedalus, on the ground, helplessly watches, and is unheard as he pleads with her not to fly so high. She disintegrates as she flies through the clouds, exposed to the rays of the sun.
- There has been speculation that Swan is somehow connected to Monad.
- It has been suggested that Re-l Mayer is a clone or partial clone of Monad, created by Donov Mayer in order to draw Ergo Proxy back to Romdeau.
- Re-L and Real were both clones of Monad done while she was comatose. It isn't specified how long Monad was comatose between the destruction of Mosk and transfer to Romdeau