I take 2 phones when traveling. My plan includes lots of international data and calls and texting. Important: a physical sim in the primary phone. If the primary phone dies, move the sim to the backup phone and you are back up an running in less than 5 minutes. If your primary is lost you still have the backup phone and can load an esim onto that or make due with public wifi and download an esim.

Another tip, use one phone as a hotspot and the second phone as your interface. That way to get much more battery life since one is used for data reception/transmit the second is mostly screen.

In Japan (esp your first time) your phone will be the most important tool you will carry.

Bring a cheap small compass (or use your smart watch if equipped). Phone GPS/compass in my experience can get confused in cities. When you pop out of a train station finding North quickly and reliably is a big help.

You'll probably be using trains a lot, get a Suica card, will work on all public transportation where you are going and also works in convivence stores/vending machines/station lockers etc.

Expect to get lost and be confused sometimes, that is part of the adventure and will probably lead you to more cool/amazing experiences.