Can I teach English in Japan?

Hello.
I'm an ESL teacher in Vietnam and of course I'm Vietnamese. I have had eight-year experience in teaching English to various types of learners from kindergarten to undergraduate, including TOEIC, IELTS, TOEFL Primary and TOEFL Junior preparation courses.
I have a bachelor degree (3.2/4) in English Language Teaching, IELTS 8.5 and TOEIC 980. I'm thinking about DELTA or MA in Sophia University to enrich my resume too. Currently I'm working in a well-known primary school in Hanoi where English is used all the time.

Am I eligible for an ESL teaching post in Japan as a non-native speaker?

Many thanks.

Best to make contact with potential employers first. Step one first, then worry about the other steps.

In terms of immigration requirements for a work visa, your background fulfills them, as you have both a bachelor's degree and more than three years of ESL teaching experience. Having either one of them is the requirement.

Of course you will need an offer from an employer in Japan, who likes your skills and experiences enough to make a job offer and sponsor you for a visa. When it comes to that, it will depend on how well you present yourself at interviews, how much of a demand for English teachers there will be at the time when you look for a job, and how many other candidates will be looking for a job as the same time as you. Some places prefer native speakers (to be considered native equivalent you need to have been educated "in" the English language for many years, which you probably do not have), other places want experienced teachers.

Reminder: there are three "visa categories" that pertain to language teaching, depending on where you teach. Each has its own requirements.

Thank you so much.