Determining factors to consider:
1. How many days are you going to be travelling this round?
2. Check cost differences of:
- Multi-city air tix
- One way Shinkansen from Tokyo to Kyoto/Osaka
- 7 Day pass cost
Calculate and take the most affordable one.
3. Since your Tokyo itinerary is fixed, you can work with the Kansai area itinerary on what you want to do.
4. Osaka has more things to see and do if you look and do research. 1 day is just scratching the surface. Please do not be misinformed.
Suggest laying out all your options and plan from there, either:
Tokyo-Kansai-SG
Kansai-Tokyo-SG
Tokyo-Kansai-Tokyo-SG
The last option, to me, is not that advisable