Defender

is a Japanese light novel series written by Chiaki Konaka, with illustrations by Hiroshi Ikuno. The series began publication on March 10, 1997 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
Takashi Ito, a young man who pretends to be a data rescue (repair of a data disk) in the back alley of Akihabara. One day, a girl asks to repair an unidentified CVD. Since then, thugs, like fighting games, have begun to appear in front of him one after another. They call themselves "Challengers". In fact, the requested CVD was a startup program to awaken Takashi as a "defender" ... What is Takashi's hidden past, and what is the identity of the mysterious girl?