Bolt Crank travels the world as the World's Greatest Mercenary. He earned that title because of his skills, as well as his ability to eat anything and then reproduce it in his right hand. During his adventures, he meets new friends, as well as his rival Hard. However, his mysterious past with a man named Leon Field comes into play later on when Shadow, a man who can control machines and calls himself Bolt Crank, and Stella, a woman who wants to mechanize every human on the planet, have Bolt go back to an old, unfinished mission he left behind long ago.