WARRIORS OROCHI 3 Ultimate

If you're familiar with most shooters' prestige systems you'll know how this works. Whenever you reach level 100 with an officer, you have the option to promote them, which brings them back down to level 1 and unlocks some perks for them. A character can be promoted up to 9 times.

For the achievement, you need to do this 3 times on a single character. This may seem like a big grind, but it's not thanks to two main things, exp. needed to level caps out at 5,000 per level rather than exponentially, and growth points. Growth points are spendable exp. so you can level characters up to eliminate grind if you want to use them. Also, various achievements and challenges will award copious amounts of growth points, reducing the need to grind those up as well.

So, the fastest way to do this would be to hoard all your growth points and get someone up to level 100 regularly. Getting to 100 isn't terribly hard if you solely use one character. Also, scrolls of enlightenment are a godsend, as they will give a small window of time where every enemy is worth an additional 300 exp.. If you have a level 100 character and enough growth points stored to be near the cap (999,999), you can promote them, then give them all the points to level to max again, promote them again, spend the remaining points to cap them out a third time, and promote them once more for the achievement. Alternatively, you can keep enough to get them back up to 70+, grind back up, then repeat with the points earned.

So first things first. To promote an officer they must first reach level 100. Once they hit that level cap, while in the camp you may go the preparations section of the menu and select the promote option. Promoting them unlocks various benefits and allows you to make your officer stronger via the upgrade stones.

For this achievement you need to promote an officer a total of three times. Getting from level 1 to 100 takes around 450 thousand growth points, so for three promotions you will need around 1.8mil growth points.

There are several ways to earn growth points quickly but in my opinion the best way is to play the survival mode. The reason being is that it appears to be glitched and, if after losing you select the rematch option the rewards will stack. So if say you get 30 wins and then loose, the first time you will get 60K GP, then if you select rematch and win 30 more before losing, you will get 120k instead. Growth points you can stack cap at 9.999.999 and it would take you between one and a half to two hours to hit that cap using this method.

What I recommend doing is getting to 30 wins and then, once the game transports you to the next map, simply keep jumping off until you kill yourself. A single run will take you anywhere between 4 to 7 minutes depending on how good your setup is and the reward table would look like this:
run 1 = 60k / 60k total
run 2 = 120k / 180k total
run 3 = 180k / 360k total
run 4 = 240k / 600k total
run 5 = 300k / 900k total
run 6 = 360k / 1.26m total
run 7 = 420k / 1.68m total
run 8 = 480k / 2.16m total
run 9 = 540k / 2.7m total
run 10 = 600k / 3.3m total
run 11 = 660k / 3.96m total
run 12 = 720k / 4.68m total
run 13 = 780k / 5.46m total
run 14 = 840k / 6.3m total
run 15 = 900k / 7.2m total
run 16 = 960k / 8.16m total
run 17 = 1.02m / 9.18m total
run 18 = 1.08m / 9.99m total

There are faster ways to earn a quick 300K or so growth points, however since with this method the rewards grow exponentially, on later runs the growth points per minute ratio becomes far superior to any other method. And since as you play the game you'll want to promote your officers more and level up new characters you unlock I highly recommend using this method over any others.

Also, if you want a good character/card setup to make your runs go faster, check out my guide for the Survivalist achievement. Good luck.