According to the result thread in GM, Misaki retired due to cramp.
This summer has on the whole been really disappointing and this loss must be heartbreaking for her after fighting so hard to have to end it this way, but she really ought to be proud from the heart and courage she showed, saving 6mps in the second set.
Misaki has had a rough year, she started with an injury a very poor clay season then came wimbledon and made it to the 3rd round and then again a very poor hard court season but that wimby result has helped her to get to the main draws of wta tournaments. She has been working hard she posts in her blog positive things when she lose, i like her attitude. And now she is in Osaka and she took out COCO 6-4 6-4, i think she has improved but hasn't show it cause of her lack of confidence but next year i see a very good year for misaki )