Hail to the Qing Guide

Only around 1.5% of all Players have this achievement so I would like to help you by sharing those tips with you guys.

1. Pick Manchukuo and turn off Historical AI -> Japan needs to go down the democratic path
2. When Japan is about to launch the democratic coup you need to do the focus Obedience but wait a few days. It still needs to progress when Japan finished it's civil war focus
3. After the Civil War fires you become a free nation with Mengukuo being your puppet. Similar to the German rhineland exploit you can now bypass the focus Assertiveness and continue to go down both parts of their focus tree. You just need to wait for Obedience to finish.(after you bypassed Assertiveness)
4. From now on I would recommend going down the right side of the focus tree and you should rush the focus "Offer Vassalization" -> The warlords become your puppet.

Since you have access to your whole focus tree your industry will build up faster than usual (Focuses like 5 Year plan help you out)
And from now on build up your army and kill China. At some point Japan will attack you too but since you own almost all of mainland china just deal with their small ports and they should offer you peace. Then annex your puppets and you are free to proclaim the mandate of heaven.

Yup, that's it