Okay, so remember Shinji's mom??Yui Ikari?? Her soul is actually trapped inside of Unit-01. They thought it was an accident but she did it on purpose so she could be eternal proof of humanity's existence.
Oh, and Asuka's mom??? Check this out. Her mom did the same contact experiment as Yui Ikari did, but the part of her soul that cared and loved for Asuka got trapped inside of Unit-02. Crazy right.
Oh and babe? The Eva units are NOT robots. They are living creatures with mechanical components incorporated into their bodies.