Diaoyu not Ryukyu, not Japan

Japan asserted that it holds sovereignty over the Diaoyu islets because they were part of Ryukyu, but actually in history they were never part of that chain.
Also the Ryukyu Chain was an independent kingdom that paid tribute to China, whether being part of Japan is questionable, which just because the US placed it to be controlled by Japan (The Ryukyu Chain has its own long estabished culture and people, which is different with Japan.)
In official documents of the former Ryukyu Kingdom, they clearly recorded the Diaoyu Islands were never part of it.