The frames you need to be concerned with for this trophy are the frames used in Vs mode.
Going through the game will unlock all but 3 frames: Aumaan Anubis, Inhert and Naked Jehuty.
AUMAAN ANUBIS: Capri Canyon -
In order to get this frame you need to start a new game with all subweapons unlocked. As you are going down the path on the right you will notice after either the second or third archway another right you can take. Go down that path and take out the enemies. If you didn't get it on your first run, there is a Ex Mission against the fallen rocks.
Get on the ground, and whip out the Vector Cannon. Your target: the rocks dead ahead. Hit the wall and watch the path open.
Once inside you will face a few enemies, then proceed to the next room where you will fight Aumaan Anubis again. No worries though - he is not tough at all, ESPECIALLY if you picked Naked Jehuty.
INHERT: Underground Tunnels - In the second area, along a few of the extending tubes that will crush enemies, and YOU if not careful, you will see this guy. He actually sits out like a sore thumb if you keep your eye out for him.
NAKED JEHUTY: Fortress Aumaan - After you get through the sixth room, and go down the descending tunnel
RIGHT BEFORE THE ENERGY CORRIDOR/CANNON EVENT, you will see two tunnels going further downward. 1 tunnel is bringing up carts while the other is taking them further down. You will also see red lines along the tunnels indicating that you can not pass through them.
Shoot the tunnel on the right and the red beams disappear. Proceed down and you will face Naked Jehuty. Defeat him and his frame will become available in the center of the room.
PLEASE NOTE: It has been reported that you can not obtain Naked Jehuty while playing as Naked Jehuty. I am not certain if that is true or not, but I played it safe and used Jehuty Ver 2 on my second run. If anyone can confirm or deny this it will be greatly appreciated.After you get the 3 frames, and the trophy doesn't pop, do not worry: you need to go into the Vs screen in order for the trophy to unlock.
Question, corrections and neg vote justifications in the comments below.