I was actually planning on this (ish) in my Imjin War timeline. Manchus take over Korea, but the Chinese push them out of their homeland, Manchuria, in an attempt to subjugate them.
The Manchus eventually have huge population pressures, and after losing against the Chinese, invade the Japanese islands. Note that they don't even take Honshu - only Satsuma, and they later lose that too.