Even the most basic framework of Japan's approach to gun ownership is almost the polar opposite of America's. U.S. gun law begins with the second amendment's affirmation of the "right of the people to keep and bear arms" and narrows it down from there. Japanese law, however, starts with the 1958 act stating that "No person shall possess a firearm or firearms or a sword or swords," later adding a few exceptions. In other words, American law is designed to enshrine access to guns, while Japan starts with the premise of forbidding it. The history of that is complicated, but it's worth noting that U.S. gun law has its roots in resistance to British gun restrictions, whereas some academic literature links the Japanese law to the national campaign to forcibly disarm the samurai, which may partially explain why the 1958 mentions firearms and swords side-by-side.
Of course, Japan and the U.S. are separated by a number of cultural and historical difference much wider than their gun policies. Kopel explains that, for whatever reason, Japanese tend to be more tolerant of the broad search and seizure police powers necessary to enforce the ban. "Japanese, both criminals and ordinary citizens, are much more willing than their American counterparts to consent to searches and to answer questions from the police," he writes. But even the police did not carry firearms themselves until, in 1946, the American occupation authority ordered them to. Now, Japanese police receive more hours of training than their American counterparts, are forbidden from carrying off-duty, and invest hours in studying martial arts in part because they "are expected to use [firearms] in only the rarest of circumstances," according to Kopel.
The Japanese and American ways of thinking about crime, privacy, and police powers are so different -- and Japan is such a generally peaceful country -- that it's functionally impossible to fully isolate and compare the two gun control regiments. It's not much easier to balance the costs and benefits of Japan's unusual approach, which helps keep its murder rate at the second-lowest in the world, though at the cost of restrictions that Kopel calls a "police state," a worrying suggestion that it hands the government too much power over its citizens. After all, the U.S. constitution's second amendment is intended in part to maintain "the security of a free State" by ensuring that the government doesn't have a monopoly on force.