In most cases, yes—if your phone supports dual SIM (for example: one physical SIM + one eSIM, or dual physical SIM depending on the model). Many travelers keep their home SIM active for their phone number and use the Japan Travel SIM for data.
If your phone only supports one SIM at a time, inserting the Japan SIM will temporarily replace your home SIM until you switch back.
If you want to keep your home country’s SIM active while you travel in Japan, you can also check out our Japan Travel Pocket WiFi, a portable Wi-Fi device that works like a normal WiFi router. Please check the details here.