Visas are not required when applying for landing permission at a port of entry in Japan in some cases.
Check the following web site to see if this applies to your case:

Exemption of Visas : http://www.mofa.go.jp/j_info/visit/visa/

If your passport is not from one of these countries, please check the following web site:
Documents to Be Submitted with Visa Applications http://www.mofa.go.jp/j_info/visit/visa/short/other_visa.html

If you need an official letter of invitation to obtain a visa to Japan, please send passport details including full name, nationality of passport to tokyovisa@tokyo2010.org and we will work with you as needed to secure your Japan visa.