From Tokyo or Osaka, Japan you can apply for a visa to Vietnam. Visiting an embassy or travel agents may cost you around 6000-8000 Japan Yen (56-75 USD) while applying for a visa on arrival may cost less at hassle and trouble free.

Visa on arrival - Visa at embassy comparison chart

Vietnam embassy in Tokyo

50-11, Motoyoyogi-cho Shibuya-ku, Tokyo 151, Japan
Phone: +81-3-34 81 6354
Fax: +81-3-34 66 3391
Email: vnembasy@blue.ocn.ne.jp

Consulate General of Vietnam in Osaka

Estate Bakurocho Bldg. 10F
1-4-10 Bakurocho Chuo-ku, Osaka, 541-0059, Japan
Phone:+81-6 6263 1600
Fax:+81-6 6263 1770
Email:tlsvnosa@gold.ocn.ne.jp

You can also apply for a visa on arrival which seems the cheapest and easiest way to get a visa to Vietnam from Japan. The total cost is from 35 - 50 USD/person. Click here to see how it works.