the fascination is not with taiwan, it is with making china whole again.
Taiwan was ceded to Japan by China as part of the Treaty of Shimonoseki (馬關條約) in 1895. I am not sure why you believe that Taiwan is still a part of China. Even after Japan's surrender in 1945, Taiwan was never officially given to China as many people seem to believe. China ruled Taiwan for 200 years. Considering that China has been around for several millennia, I hardly think a 200 year stint under Chinese rule qualifies Taiwan as China's birthright which she needs so she can be "whole again."