She is completely self-taught, enjoys reading shonen manga and was "discovered" while working as a secretary. Kojima is famous in the west for her work on the Castlevania franchise, even though she has mainly worked creating the artwork of many novels, both as cover and interior artist.
She has worked with renowned authors like Kikuchi Hideyuki (better know as the creator of the Vampire Hunter D series) as well as creating the art of many yaoi hardcore novels (even though her art in those kind of materials is not "graphic", just "suggestive"...)