Well put, Hindu. Johnny is an often overlooked character of Chrono Trigger. But, unlike many of the game's other puzzles, I think this one is easily solved. Japan has a fascination with the post-apocalyptic dystopian technopolis, which of course is 2300 A.D. Chrono Trigger to the hilt, and one of the common archetypes that populates these blasted, sprawling urban scapes is that of the young, energetic leader, typically of a shoddy gang of streetsmart, world-weary peers. Almost always a male, he has a righteous attitude and a sense of a honor that makes him more than just the thug that you might otherwise take him to be if you look at his gang as a whole. He usually looks handsome, commands the respect and admiration of his followers, and, importantly, is a real hotshot with some type of technology, always new and gleaming, set apart from the decaying, endless city where they live. (I am thinking of the Kaneda's biker gang out of Akira as a good comparison to Johnny's biker gang in Chrono Trigger.) Sometimes their mods encroach into their very bodies, and they become part cyborg. This archetype, of course, describes Johnny very well. He is a classic page out of postmodern Japanese culture.
Did anyone else notice his corpse on the highway in the Dead Sea? I don't think I've ever seen that mentioned here.