All great solutions here, but what I found myself searching for was "how can I do them better", so here's a list of things the other guides haven't covered that I found on my own.
1. There are no Items you can equip that will help.
2. The "Trinity" character ability increases your True Triple gauge, but is pointless as you won't be able to include them in your roster.
3. The attacks must be done in a specific order.
4. You must build your Triple Rush gauge before you can attack. This is the blue/green bar in the bottom-left, curves up below your Musou bar. There is a sound when you hit the limit.
5. Don't die
So, here's how I did it :
1. Fire up Story Mode
2. Go to Battle Preparations / Change Team
3. Choose your 3 characters IN ORDER listed in EmporerDragon's guide above.
4. Using his first entry as my example, your last character should be Xiahou Ba. Press
5. Options / Save. This is very important. I like to do it after choosing my characters so its all ready to go if you need to reload.
6. Begin Advance, pick whatever stage you want, I've been using Rescue at Yiling out of habit. Don't choose Easy, pick at least Normal, depending on how good your characters are. For Level 1 guys I choose Normal, anything better and I do Hard.
7. Skip chat (
x2), Begin Battle (
x2). After loading, hit A then the 3 crack lines again to skip the intro movie.
8. Now wail away on enemies. Use your lowest level/weakest character you have, as the True Triple gauge seems to go up based on the amount of times you hit an enemy. Not number of kills, combo or anything. More hits on the first group of enemies, the better. It is very much possible to have a full Triple Rush gauge with only 10 kills. This means less running around to get kills, this is why you don't choose Easy difficulty. On hard with a sub-100 character you should be able to max the gauge on the very first group of enemies, if all of your characters are maxxed/Mystic, you could always buy a 1-star weapon from the blacksmith. Either that or spend 5+ minutes on the stage clearing out peasants.
Update: You can skip this, Triple Rush will use Musou, cheers Saracin
9. Once you PING and your True Triple gauge is maxxed, jump off Red Hare (as if there is any other mount), change to the third character in the roster (Xiahou Ba) and hit your
10. Wait for the enemy to flash yellow when they're hit, then MASH the Right Trigger
. Don't stop mashing until all 3 characters have had a hit and you're back to your first one (Xiahou Ba). You do not need to time these hits, mash that button as fast as you can if you like.
11. Once the sequence is complete, you won't have any popup or any kind of register that you've done the move, so press
to pause, hit the
button then go to the left and to the Achievement app thing. Not the snap, the new one that they added. I guess snap would work but I don't like it.
12. Scroll down to the secret achievement for this. It'll probably be at 1% after your first True Triple Rush. Hit
to make it your favourite so it appears at the top of the list from now on. If it isnt 1%, you did something wrong, possibly the order wasn't right. Go back to the game and try again. Your Triple Rush meter will still be full, ready to go again.
13. If the completion % has gone up, then you've done it! Go back to the game and choose Return to Camp
. Do NOT under any circumstances choose Quit otherwise your progress will be reversed. Yes, they can undo achievement progress.
14. Once back at camp, either go back to Step 2, pick the next 3 characters and continue, OR go to Options and Save your game before quitting.
** If you die, your progress will be reversed to your last save ** Always save your game before starting a stage. If you don't and you get through 5 or 6 triple rush moves, returning to camp after each one, then you die, all that progress will be reversed the next time you do a Triple Rush move!! If you think you are going to die and you haven't saved in a while, you can make use of the interim save, however keep in mind that if you die and have to resume, you lose the ability to return to the camp. You will need to see the stage all the way through to retain your progress.
Follow EmporerDragon's list to the letter and you should have this. I just wanted to include my specific steps, confirm it works without having to complete the stage (just don't "quit"), and confirm that there are no other items or anything else that will help this achievement.
For those that it glitched on, I don't have any fixes other than those listed above. Can only imagine that after doing the move, you died or quit instead of returning to camp and that progress was lost. Only the "return to camp" option keeps your achievement progress.