|Prime Field Interference Manifestation|
Prime Field Interference Manifestation
Human appearance, high physical strength, seithr immunity, all female species
A Prime Field Interference Manifestation (示現境界接触用素体, Jigen Kyōkai Sesshokuyō Sota), also known as an Embryo Storage (エンブリオストレージ, Enburio Sutorēji) or Es (エス, Esu), is a form of Prime Field Device that was created by Souichiro Unomaru sometime between 2040 and 2050.
Created with funding from the Mitsurugi Agency, all of these Prime Fields are designed with the ability to contain an Embryo, a crystallization of the Azure. The first of these Prime Fields was Es. When she was first created, Unomaru deemed her a failure because she did not contain the Embryo within her. However, she was eventually transferred into Sleipnir to hunt Drive Unions and to gather first-hand information on the Legacy Weapon - Signati Gladio Crystalis: Murakumo through its usage. Continuing the mechanical nature of the Es line of Prime Fields, Es was equipped with a sensor that allowed her to track Discover Calls, a unique sound emitted by Unions. 
Because of Es's rare emotional behavior and eventual failure, Unomaru began work on the Es-N line of Prime Fields, but the majority of them were destroyed through the combined efforts of Touya Kagari, Mei Amanohokosaka, Kuon Glamred Stroheim, and Es. Only the ninth unit remains, but it is under Mei's command. 
There are several large differences between Es and the Es-N. As a rule, both Es and Es-N are designed to be methodical and infinitely loyal to Unomaru, but Es alone remained open to reason, something her successors were not. Similarly, Es looks physically human, while the Es-N look and act far more mechanical in both mannerisms and appearance. 
The former is made out organic materials, while the latter is made of inorganic materials and incapable of thinking for themselves, instead having a hive-mind connected through the cloud. Es is also designed to rapidly disintegrate after not receiving maintenance for two days as her body would stop functioning. Both are unable to continue without maintenance for extended periods of time, eventually running out of energy.
The Es-N line was fuelled by the Crystals of Unions, although this was condemned as morally wrong and changed with the ninth and final unit by Mei, who powers it with magic and electricity. The Es-N line is also stronger than Es herself because of their swords, which were created with Mei's blood, giving them the ability to control the flow of seithr.
Through inheriting the Embryo from Hinata Himezuru, Es was able to utilise its powers to create the World of Tsukuyomi. After falling into depression from the deaths of her friends, Es discarded her memories and transformed her body into Nobody, who is still considered a Prime Field since she still contains the Embryo within her. Through the help of Nine the Phantom, Es was reincarnated into a human and sent back to her own time, while the Prime Field that was once Nobody remained within the Phantom Field with the Embryo still within her.
Es was summoned by the Amaterasu Unit into the BlazBlue world, well over 100 hundred years after her own time. It is unknown if she is still a Prime Field Interference Manifestation, but it is clear that she is no longer human.