I'm not sure if this is a territorial gain, but Korea gained independence from the Sino Japanese War (Japan's interests in Korea were recognised with the Treaty of Portsmouth).
Also, Japan gained the southern part of Sakhalin Island, Taiwan, Pescadores Islands and the Liaotung Peninsula. There was the Triple Intervention which meant it had to give up the rights to the Liaotung Peninsula to Russia (but it was eventually taken back with the Russo Japanese War).