Implications for registering as resident when visiting Japan

Hello all,

EU citizen here married to a JP national and living in Europe.
Every year we tend to visit Japan at the start of July so that our son can spend some weeks attending school and experience Japanese school life a bit and build a bit of a link with the country.
When we visit my partner and son register as residents for this reason and unregister at the end of the trip.

I was wondering if there are any hidden tax or estate traps in doing so?
Thanks for your insights in this matter.