You need an embassy visa for Japan if you have a Vietnamese passport
Visa options for Japan (2)
Electronic visitor visa may be available for Tourism
Travelers need a visa to visit Japan for Tourism. A Japanese eVisa is the fastest and easiest way of obtaining a visa for Japan because travelers can submit their applications and supporting documents online. Once the application is approved, travelers receive their eVisa confirmation electronically. Travelers can apply for Japanese eVisa only if residing in the following countries: Brazil, Cambodia, Canada, India, Mongolia, Saudi Arabia, Singapore, South Africa, Taiwan, United Arab Emirates, United Kingdom, and the United States of America. Vietnamese passport holders living in Vietnam can apply for Japanese eVisa through Travel Companies designated to organize package tour groups for a maximum stay of 15 days in Japan. Different application pathways depending on the country or region the traveler is applying from. See the source for more details.
This is not offered by sherpa°.
Apply on the government site.
Visitor visa
Travelers need a visa to visit Japan for Business or Tourism. A paper or embassy visa is the only visa available for travelers visiting Japan. The visa is typically a stamp or sticker added to the passport. Travelers must obtain this visa from a local embassy, consulate or visa center before traveling.
This is not offered by sherpa°.
Apply on the government site.