Japan runs on 100V mains power with Type A/B style outlets.
Most modern phone, laptop, and USB chargers are rated for 100-240V input and handle regional voltage differences automatically — the only thing that actually needs adapting is the physical plug shape, not the voltage itself. The exception is high-wattage appliances without auto-switching power supplies, which are uncommon in portable electronics.
What to pack
A simple plug adapter for Type A/B outlets is sufficient for virtually all modern USB and USB-C chargers — a bulkier voltage converter is rarely needed for phones, laptops, or cameras.