Work Visa as an American Citizen

I'm afraid you can't apply for it in Tokyo if you don't have a residence permit there. According to the website of the visa center in Tokyo, non-Japan citizens shall provide documents that entitle them to reside for an extended period of time in Japan provide original and photocopy. Temporary visitors to Japan should apply for a Chinese visa in their own country. For the special cases, consular officer has the rights to make the final decision on whether issuing a visa or not.