Chinese embassy in Seoul requires a ARC be valid for more than 6 months for visa application to China. As what I understand, you will visit China after your contract is up, that means you will not return to Japan, right? In this case, you can try to hacdle your China visa through a travel agency Busan, where they issue visa to applicants whose ARC is valid for less than 6 months. Or you can just send back your application to US, let your family help you with this when you travel to other countries(time enough for mailing back your visa and passport). Moreover, you can read China Tour(https://www.travelchinaguide.com/tour/default.htm) to better arrange your visit in China.