This one is a little tedious, you have to use Amane Astral Finish in EVERY playable character. Unlike the Taokaka achievement, this one needs also that you are in the last round a match (you can change Vs. Mode to 1 round in options), the opponent have his lifebar red (less than 35% of health), and have 100% of Heat (Super bar). Then when all the requirements are set, press ↓↓↓ D close to the opponent and you will activate the Astral Finish. This Astral will transform each character in a younger version of them, there are some neat references to the story as well (The Platinum one is my favorite) There are 28 characters, have fun looking at each one of them!