JRPass in Kumamoto

Hello,

I will go to Japan in March and my itinerary is as follows:

Tokyo > Osaka > Kumamoto > Okayama > Hakone > Tokyo

I will buy the 14-day JRPass which I will enable in Osaka, my question is if this pass is valid to go from Osaka to Kumamoto and then return to Tokyo or should I buy an additional one for the Kyushu area.