Depends individual. If you want it to be limited into 20kg, sure can do it. But do make sure you spare at least 5kg each for some light shopping stuff.

You may consider:
- type of clothing that you need for that particular weather, and if clothing can be recycle wearing
- will you opt for laundry
- or bring stuff for half trip, then shop for the balance. (never tried in Japan, but I did that alot in Thai)

and not to forget you have 7kg handcarry each 

I bought 20kg each for going, and coming back with 30kg (myself) & 40kg (hubby). But now feel abit stupid with the 40kg and there is no way we can drag a luggage that heavy. 

me and my hubby shared 25kg....