Cash
Legal to refuse?
Prevalence
Japan Credit Card Association data from 2019 shows that about 38% of total household expenditure is paid using cash.
500 yen coins
Japan switched to a new design and metallic composition for the 500 yen coin in 2021. The new coin is bi-metallic, with a silver-colored center. For the time being you will see both old (single-color) and new (bi-color) coins in circulation. Both are technically valid currency, however certain automatic machines (ticket machines, vending machines) may not be calibrated to accept the new 500 yen coin, so if you receive one in your change be prepared for this possibility that you may not be able to use it everywhere.