Phone works well in Japan, but it’s likely to be very expensive to use (making as well as receiving calls). As Daniele says, check the details of the plan you have.
I kept the line turned on for emergencies (I hardly get actual calls, and you can divert all to voicemail before you travel if you wish) and bought a data-only SIM for under Fr.10 from klook. That company is good for travel stuff in Asia.
With data or wifi, facetime, whatsapp etc. video calls are free (apart from the data usage, of course).
Another alternative is an eSIM as you suggest, with a local Japanese number. However, you calling that will still be expensive and your partner calling you may be expensive.