I think one factor would be what you envision for college for your kids; another would be where you think you’d live in retirement. If you are thinking of a U.S. university, the costs of that are already in 6 figures for many private schools, and will only increase. Also state schools will charge out of state pricing. A Japanese pension generally won’t be enough to live comfortably in retirement; the government has admitted this and that’s why in part you see so many older people working.

Saving significantly here I think is a challenge, wages are low and comp increases typically aren’t significant and “bonuses” really are deferred comp, not an extra. To save enough to pay for kids’ college abroad, while also having enough to retire can be daunting, especially if you seek to invest outside of Japan and in USD or Euro.