First Baby is a new character introduced in Metal Slug Attack.
The original version of White Baby, First Baby is an AI resembling an adolescent female. Amadeus locked her away in the deepest parts of his files, with no contact whatosever. This made her insane and have a desire to break her enemies apart. White Baby would eventually free her from her prison. She sees her and the Iron Fortress as her younger siblings and is very protective and affectionate towards them both.
Like White Baby, First Baby rides a platform, but uses a different attack style.
First appearing in the Extra Ops "Sky King", she is freed by White Baby and the two decide to cause some mischief by attacking a Sky King. They severely damage it, after which Navy attempts to hack First Baby, but White Baby removes the program before it can fully control her. First Baby thanks her for the timely save.
Later on in "United Front the 10th", she is seen with the Iron Fortress trying to figure out what is wrong with White Baby. She tries to look around but is repelled, before stating that she is more interested in the golden weapon heading their way. Arriving at the battlefield, First Baby helps her younger sister out.