Just finish the Final Battle of the game and the achievement is yours.
I used Cloud, Cid and Tifa for this, but it makes no difference what characters you are use. You can use what ever characters you like except of Cloud. I recommend to have at least one ribbon for Cloud. It makes the stuff easier.
Ribbons can be found in the Temple of the Ancients: You reach a room with a giant Clock. Leave the Clock at 5 there is the ribbon
and a second one is in Gaea's Cliff: Here is a video for this ribbon
(Video Credit goes to LetsPlayGGs)Sadly both are missable. If you miss both Ribbons you can Morph Master Tonberry in the Northern Crater into Ribbons.
Best alternate accessory in my opinion is the Safety Bit. It prevents Death, Death Sentence, Slow-numb, and Petrify. You can purchase those in Rocket Town for 7500Gil.
If you never played or finished Final Fantasy VII i highly recommend to watch the credits up to the end there will be a final cutscene.