A Designer Baby is a child created with artificially modified DNA.
With this it is possible even for parents who have completely normal genetics to bear a child who possesses magic circuits.
Within the world of EXTRA, Shinji and Julius (among others) are designer babies.
Contrary to what people often think, Leo is in fact not a designer baby. His great knowledge, intellect and experience were instilled through a hypnosis learning method, and his body does not contain a single speck of artificially created parts. His existence is not something that was realized through human intervention, he is just a “Born King.”