You can earn this achievement by accomplishing two others achievements in the same save file.
These achievements are :
But be warned, if you're unlucky like me, the achievement will not pop if you have rescued all the civilians before killing the last boss.
If it is the case, beginning a second save file will not allow you to earn it. You must delete your save file (from the console and the cloud) and the game as well and then download it again.
After that, i recommend to do all the game and completing all the missions with 100% but not the very first one (Shell City) and doing at 100% this mission after having done all the rest of the game at 100%.
In two words, choose to deliberately not save all the citizens before fighting the last boss.