The country's homicide rate is associated with a stable and prosperous society with low inequality and high levels of development. Young Japanese males now commit only a tenth of the homicides committed by their predecessors in 1955, and the age and sex distribution of victims tend to be uniform across age groups. This has been attributed by some researchers to, amongst other factors, extremely low levels of gun ownership (1 in 175 households), a greater chance of detection (according to police data, 98 per cent of homicide cases are solved), the rejection of violence after the Second World War, the growth of affluence without the accompanying concentrations of poverty common in many highly developed countries, and the stigma of arrest for any crime in Japanese society.
Unlike the U.S., Japan has strict gun laws. Most guns are illegal, and there are tight restrictions on purchasing the few firearms that are allowed in the country, according to The Atlantic. Japan also has a rigorous testing and background-check process for those who seek to purchase a gun.
To put it all into perspective, the U.S. saw more than 12,000 firearm-related homicides in 2008, while Japan had only 11.
http://www.businessinsider.com/why-japans-murder-rate-is-so-low-2014-4