For this achievement you have to complete every mission without dying and reloading the last checkpoint, failing quick time event's does not effect this achievement, I failed plenty.
So if you die you have to restart the mission.
Your best trying this after you have fully upgraded everything and completed the game on hard to obtain the 4th Ninjutsu, plasma shield. With full upgrades this should be no problem on easy.
To unlock easy difficulty just die 10 times in a row