So are you saying being the first to land troops somewhere is the only requirement to declare something as yours?

No one owns it because it's disputed. Taiwan's claims are just as legitimate as anyone else's. Read up on the history of the islands. It's no more Japan's than Taiwan's or China's, that's why it's disputed and it's hard to settle the dispute.

What is absolutely true is that Japan currently administers it, and neither Taiwan nor China likes it.

What makes Japan's claim any more legitimate than Taiwan's or China's? The fact that they started administering it formally as part of an imperialist period in their history in the late 1800s?

I get China bad, but let's not let that cloud everything to the point of historical revisionism.

Japan effectively annexed the islands during the first Sino-Japanese war, prior to that the oldest historical records even vaguely suggest any claim comes from the Chinese side.

To say that Japan 'administered' the islands since the late 1800s when they basically claimed it as part of a broader imperialistic war and then claiming this is Chinese imperialism in action is just wrong.