In the immigration procedure in Japan, all international visitors must present a valid passport, and Visa excluding some exemption countries. Please search for relevant information on the website of Ministry of Foreign Affairs of Japan and take essential procedures for you. Some useful links to the MOFA websites can be found as followings.
Exemption of VISA (Short-Term Stay)
Border enforcement measures to prevent the spread of COVID-19
A letter of invitation can be provided upon request. Please apply for a letter of invitation when you register the conference through the registration system.