All participants need a valid passport to enter Japan.
And also, participants from certain countries that do not have the visa exemption agreement with Japan must have a visa issued by the Japanese embassy / consulate in their countries.
Please check the visa exemption list: http://www.mofa.go.jp/j_info/visit/visa/short/novisa.html#notice01.
For those who are not on the visa exemption list, they are required to prepare supporting documents from Japan.

The conference organizing committee will provide “required documents for visa application to enter Japan” to participants whose countries are not in the list, and who completed conference registration and submitted the following documents via e-mail:

1. Copy of passport identifying name and photo
2. Document certifying the participant’s institutional affiliation and position such as staff or student ID card, etc.
3. Copy of air ticket with itinerary
4. Confirmation of hotel reservation
5. Filled visa information form

Upon the receipt of all documents above, documents for visa application will be issued and sent to the applicants.