Living a student/backpacker life in Tokyo in a 20sqm room and shared bathroom is easily possible on 200,000/month.

Bringing up a family, paying medical, saving money, schooling etc. in Tokyo on that is going to be mighty hard. You'll be living probably a 1.5-2 hours commute out of Tokyo (assuming you work there). Osaka and other cities are somewhat (but not massively) cheaper.