On March 6, Super Junior announced via their official Japanese website, "Due to the Japanese government's temporary new law placing all visitors who arrive in Japan from South Korea in a 2-week quarantine period, 'Super Show 8' in Saitama has been postponed."
While many K-Pop artists and agencies have already cancelled or postponed their overseas events in light of the global Coronavirus threat, Super Junior were scheduled to continue on with their 'Super Show 8' world tour with a 2-day stop in Saitama, Japan from April 25-26. However, on March 6, the Japanese government newly announced a temporary quarantine restriction effective beginning this March 9 until the end of this month, inevitably cancelling or delaying most K-Pop events scheduled in Japan for the rest of March.
Meanwhile, numerous K-Pop artists are also scheduled to perform in Japan for 'KCON Japan 2020' soon, taking place from April 3-5 in Chiba, Japan.
Sad to hear it but it's for the best.