She is another creation of Dr. Gero with the destiny to
destroy Son Goku. Kuririn fell for her after his first encounter with her.
She was unable to escape the persistance of 2nd stage Cell to become 3rd stage
("Complete Form"), and was finally engulfed by him to achieve his
dream of the "perfect fighting machine."
We don't see #18 again until after Cell was nearly destroyed by Son Gohan and
spits her back out. Kuririn "rescues" her and they subsequently
settled down with a daughter.