Is OSA the same airport as KIX? I've not heard of KIX or ITM being referred to as OSA before.

I have travelled extensively around Tokyo with a wheelchair and travelled around Osaka a little as part of a solo rehabilitation trip (there is nowhere on earth I would feel more comfortable and secure in order to go and recover the use of my legs than Japan).

I travelled from NGO (Nagoya) to Osaka but haven't been on the train from KIX to Kyoto.
However, there are plenty of photos of the Haruka train (KIX to Kyoto) on the internet
http://kurt.sauer.us/wp-content/uplo...a-carriage.jpg
They are clear enough that I can confidently say that you will have no problems using a wheelchair on this route. Both KIX and Kyoto stations have wheelchair access to the train platforms. When travelling by train with a wheelchair you will need to enter the station via the inspector's desk rather than through the automatic turnstyles. It is unlikely that the station staff posted here will speak any English but they will probably be asking if you require assistance.
The assistance they can provide may involve a portable yellow ramp to help you get onto the train. If they are aware of which station you are travelling to (and even if you don't speak each others language you can still get this across easily) it is likely that the station employee will call ahead for someone to meet you and help you disembark.
But even if this doesn't happen, other passengers are likely to pitch in if you need a bit of help.
For instance, my husband is quite strong and has a lot of experience with moving fragile and heavy (and priceless) objects so we never really needed the yellow ramp service. But it does make it easier to board a train.

If you were to travel back from Kyoto to NRT/Tokyo I can assure you that this trip can also be done with a wheelchair.