By no means easy, but if you have the right tactics, this will come.
The first thing to note, is that this is NOT accumulative over challenges, and can only be done on the mission:
"The Omega Program"
First, choose to play as "The Rising Sun" and make sure you have unlocked most of their units and defences.
Now, build up your base defences.Two defences to each access point should be enough. Next build several Chopper VX's. (6 or 7 should be enough) Now take these Chopper VX's and take down the enemies Construction Yard's and Dojo's doing this cripples their ability to produce more buildings and more "Yuriko clones", making it much easier for you to accomplish this achievement.
By the time you have accomplished this, there should be roughly 20-30 "Yuriko Clones" on the map. Now you simply need to just hunt them down and eliminate them, but remember to be on your guard as the A.I may simply send all the Yuriko Clones against you in one swift and most likely fatal attack.
Another option you can take is follow the same set up, except you wipe out two of the three enemy bases.
And just put all your units outside the enemies final Dojo and simply wait for Yuriko clones to be trained, and simply killing them when they spawn from the Dojo.
Hope this helps.