In ancient China, the common custom would be to have a political marriage, therefore the 'hostage' would probably be part of the extended royal family. Like during Han dynasty, Liu Bang started the tradition of marrying princesses to the Xiongnu in a bid for peace after he lost against them. In the three kingdoms period, all three were related to each other by marriage - Cao Cao's niece married Sun Kuang, Sun Quan's younger brother; Cao Zhang married Sun Quan's cousin Sun Ben's daughter; Liu Bei married lady Sun; and Zhang Fei married Xiahou Yuan's niece. [source: Book of Han, Records of the Three Kingdoms]

Sometimes, the winning kingdom in the previous engagement may demand that a prince (since sons were more important than daughters) be sent to the capital of the kingdom to take on a 'post'. That would be a more direct demand of a hostage, but still the selection would require someone of importance (namely royalty) to be sent, not just any noble. Examples would be Xiong Wan, crown prince and later King Kaolie of Chu; and Ying Chu, prince and later King Zhuangxiang of Qin (the father of Qin Shi Huang).