Michaela (ミカエラ, Mikaera?) is an alias to refer a specific kind of vampire named, and possibly, created by a second progenitor known as Saitō. Some are speculated to have the Seraph gene. This feature is explored in Seraph of the End: The Story of Vampire Michaela.
According to Ferid he became Saitō's "angel" when he chose Ferid, and that, from that day forward, he would be a Michaela, Saitō's angel but there were others thought to possess the Michaela Trait.
The Michaela trait only appears in one out of tens of millions of boys prior to the apocalypse. After the apocalypse, it is nearly impossible to find one. There was one whose body was kept by Sika Madu during the dark ages of Greece, one that Noya, Krul and Ashera were figuring out what to do with. There were also those who were thought to have the Michaela Trait.
Currently, the meaning of the trait is unknown.
The story goes back to the origin of vampires when the angel Michaela fell to the earth.
Starting about 150 years before Crowley meets Ferid, Ferid watches and waits for him to be born. Ferid uses Saito's blood to turn Crowley into a vampire during the 13th century. He does not mention the term Michaela to Crowley, but he tells Crowley he was watching for him long before he was even born. He says he uses Saito's blood instead of his own in order to make Crowley much stronger and more akin to a brother than a servant.
During the 21st century, Ferid manipulates Krul Tepes and Mikaela Hyakuya and manages to have Krul turn Mika into a vampire. Mika is also one of the Seraph of the End, who was previously experimented on by the Hyakuya Sect.
Michaela is mentioned by Ferid to Guren, Mika and Crowley as he explains when he was human, that it is Saito who gave him the name and made an angel. After being abandoned by Saito, he tells Mika he is his new Michaela. Later it is believed that Mika might be truly a Michaela being.