Oneworld is weak in service to China, partly due to CX having to operate chinese flights using Dragonair (partly CX owned but not part of Oneworld). Recently CX has received some rights to fly into several chinese cities, so depending on the date of your service it may be possible to fly CX HKG-PEK (but very few flights allowed, I think it is only 3x per week to start). Nothing PEK-NRT so you will have to buy that separately and open-jaw your ticket. Look on http://www.cathaypacific.com and download the PC timetable for Oneworld; this will help with your planning.