The EDB have a teacher registration team
EDB - Teacher Registration
However if you have a non-local qualification like myself - my degree is from Australia, you need to get your qualifications accreditated by Hong Kong Council for Accreditation of Academic and Vocational Qualifications (HKCAAVQ) before going to the EDB. See website Welcome to HKCAAVQ cost is around HK$2000.
If you have prior working experience overseas i.e. in your case Japan then international schools may be interested depending on how many years you have been teaching. It varies from school to school.
For example, I have only 1 year so am having to go supply teaching until I get a full time position just to get the experience.
If looking for an specific ESL job - some schools will see it as an advantage if you have ESL/TESOL etc certification.
Hope this helps.
p.s. hiring for international schools/ESF for the next academic year has mostly been concluded. If there are any vacancies - generally maternity leave/temporary teaching positions. Check out the classified post www.classifiedpost.com.hk or ESF website www.esf.edu.hk.