From Justmanga.com:

The manga behind the cult favorite animated series seen on Cartoon Network is here! What happens when a robot suffers an identity crisis?

On the surface, Jiro appears to be a normal teenage boy — he's riddled with self-doubt, has trouble making friends, and owns a guitar he doesn't know how to play. But he's really Kikaider, a super-powered android with a secret "Gemini" device implanted in his brain to help simulate human qualities. Professor Gill, a former associate of Kikaider's creator, is hunting for the Gemini device… and he'll go to any lengths to recover it!