What documents I need apart from passport, Tickets to Tokyo and hotel stay in Tokyo ( as well as in Beijing)?

I have US passport and I will be staying in Beijing only for 2 days ( landing on March 10th around 5 PM and then taking flight on March 12th at 4:30 PM) and then staying in Tokyo for another 2 days.

It seems like I can get visa-free stay.

Thanks Much in advance for your response