Hail to the Qing
Has completed focus Claim the Mandate of Heaven
Take the Assertiveness national focus sub-branch and build your military up. When dealing with the Bandits, one of the possible ways to deal with them is purging them, which requires that you stockpile infantry weapons then click the decision. Another way is to pacify them, which requires you have six divisions on three separate states each. The best thing to do in order to get many divisions is to pacify them. This will give several divisions of cavalry divisions. In order to pacify them, change the infantry to the weaker 3 infantry units. Train more divisions and bring the trained divisions on the field. Then, switch the cavalry to the weaker divisions. If done properly, you will only need to do one bandit event. When the Bolster Nationalism focus is reached, it is possible to recruit the cavalry from the decision and then change it to manpower by disbanding if necessary.
After dealing with the bandits, switch the divisions to the 6 infantry unit divisions. It is not necessary to upgrade the template because if you take the Staff the Court With Manchus focus then the Expand the Imperial Guards focus will give 20 width 7 infantry and 2 artillery divisions. Make sure to research artillery so it is possible to reinforce them. Build a strong army and place them on the Korean border to the east and the Mengkukuo/ Japanese border to the west. Manchukuo may join the war against the Chinese but do not help. This is so the Japanese will be weaker when Manchukuo goes to war with them. Wait until Japan weakens China (when Japan controls most of the coast) to take the Independence War focus. If the Japanese are close to your border, it indicates that they both haven't fought long enough.
Once ready, Take the Independence War focus and take all of Korea first. This is so that there will only be one front needed to fight in. Have garrisons in the ports so the Japanese don't naval invade. Take as much Chinese territory as possible. This is because if China surrenders, Japan will take territory belonging to the Chinese not under Manchu control. This will also give them more surrender progress against Manchukuo It may be beneficial to take the Offer Vassalization focus to vassalize the warlords if the war is going badly. be aware that you have to annex the warlords afterwards via the puppet mechanic introduced in Together for Victory. Peace out with China first. This way, Manchukuo will control if Japan would white peace after they get kicked out of Asia or not. Once China has surrendered, annex all land and push Japan out of Asia. To take the Mandate of Heaven focus, you will need all of mainland China minus the European treaty ports so annex all of the warlord puppets if there are any. For The Dragon Swallowed the Sun achievement, do not let Japan peace out as you will need to annex them.