There is no one else who can do it and there is also the face issue -- if China switches leaders after just two years it will be an admission that their first choice was wrong.
Chinese leaders do not want to allow the society's sentiments to affect the complete control of foreign policy and they also understand that nationalism can be a double-edged sword,
Japan is certainly eager to improve relations. On the other hand, China also realizes that its ties with Japan are essential for regional stability, China's economy, and so on. If leaders can avoid provocative statements and actions, ties can improve.
A new prime minister will always have an opportunity to make a fresh gesture to improve relations. And I think Chinese leaders would also like to seize the opportunity.
(Beijing) hopes to establish legal basis for (its) Taiwan policy ... and Chinese leaders want to establish a base line.