RetireJapan

What happens if the account holder of a Junior NISA account becomes a non-resident of Japan before they turn 18?

That is a really good question. I don't know the answer, but presume it is similar to what happens with iDeCo.

Anyone else?

I asked this question of Nomura, which holds my children's Junior NISA accounts. They said that if the account is dissolved before you could withdraw funds you must pay back the taxes which were not paid during the term of the Junior NISA. That was the response of the nice young lady on the phone and I have not actually had to do that but I am assuming they are correct. From the time your child turns 18 you can begin to withdraw Junior NISA funds (according to my understanding) even though the accounts themselves last until the child is 20.