There is no "continent" rule as such in a *RTW, however you can only travel from IATA area 3 (Oceania/Asia) to area 2 (Africa, Mid East, Europe) or v.v. once per itinerary/ticket. As you have done this with your KIX-VIE segment, you can't come back into area 2 from area 3, but you aren't in your example - you're entering from area 1.
You are quite within rights to stopover in Asia again - mileage pending of course - and I can't see much else wrong with your proposal under rules problems.
Cheers.