Melissa "Issa" Karas is the protagonist of the comic Replica. She is a 15 year old girl who lives with the Professor in New York. She posesses shape shifting abilities and uses those powers to fight evil.
Issa is brash and quick to judge, although this can be attributed to her being a teenager. Ever since her father disappeared she is obsessed with finding him and more often than not gets herself into trouble due to her recklessnes.
It is not known how she came to know the Professor but she considers him something of a friend or father figure and despite their differences, she is glad to have him.