Most nationalities can enter Japan visa-free for a short term stay. A short term stay is up to 90 days for tourism, business, visiting friends or relatives etc that does not include remunerative activities.
There are currently 68 countries and regions for visa exemptions including USA, Canada, Australia, New Zealand and the UK. However, please make sure you always check your visa conditions prior to booking a flight, even if you are from a visa exemption countries/regions. You can read more about how to obtain a visa on the official Japanese Ministry of Foreign Affairs
Safety in Japan
Japan is a very safe country and crime levels are low across Japan. Japan is a safe travel destination for solo and group travellers. The majority of visits to Japan are trouble-free. Always buy travel insurance before arriving in Japan.
As with any destination, you should maintain the same level of vigilance and practice common sense. It's safe to walk at night and to take public transport.
Tokyo's entertainment districts are considered at higher risk for crime. Avoid entering clubs and bars in the Kabukicho area without a guide or a local who you can trust. Take steps to ensure your drink cannot be tampered with.
Don't accompany street touts to any bar or establishment. In case of emergency call 110 for the police and 119 for the fire and ambulance services. Remember that hospitals might need to confirm that you have valid insurance before admitting you as a patient.
Road travel is safe and you must adhere to all the rules and regulations. Remember to have all the correct documents with you at all time as the penalty for driving in Japan without the correct documents are severe.
Remember that there are some exclusion zones around the Fukushima nuclear power plant. The areas are identified by the Japanese authorities and kept up to date.