In Agarest Generation of War Zero, we find out Mimel is actually a different from of life created by the Deeth, the Goddess of Fate one of the Gods of Darkness, as a form of "entertainment" for the Sovereign of Night Chaos in the visage of the High Goddess Varna who Chaos loved but ended up marrying his Brother Lenion, the Highest God.
Because of Deeth's perverse nature we can assume she meant it in a perverse way however Mimel reveals however that Chaos was kind and fatherly to her, however due to her reminding him so much of Varna Chaos had Deeth take Mimel back, the God of Time and Space Mobius was able to get Deeth then give him Mimel to use in his plans.
In Agarest Generations of War 2, Eva is revealed to very close to Chaos, when her own memories return she starts talking about how she didn't "want to be abandoned" which is how Mimel's alternate personality Mimi felt. In the True End when the party faces Deeth, Deeth comments on Eva's "Current Appearance" and it having been a very long time since the 2 had seen each other, also Chaos is shown to be very caring of Eva when he shows up.
Considering that both Mimel and Eva look human but did not age between Generations and had no traits that would prevent aging (apart from being a unique race created by Deeth), are they actually the same person?