Did you read this from the beginning? This story is based on biblical lore, with the espers being scientifically bio-engineered humans created from the dead body and dna of an actual biblical angel. Because of this, all the espers were given names associated with angels from the Bible. Michael is the chief archangel and leader of all angels in the Bible, so since Eve was the very first one to be created, he was given the name Michael originally and that was his name while he remained active as an esper. However when the war ended and the espers started being socialized with other humans, they were given new names in order to separate them from their esper personas, so Adam named Michael Eve.

Wait why is eves name micheal? And bro adam needs to chill he looks so tired from guiding with those eyebags