There are several Tifa dresses and or costumes to unlock, 3 to be precise and getting them all will count towards the Dressed to the Nines trophy achievement which requires you to Obtain all nine bridal candidate outfits.
In order to unlock different ones you will need to complete all of the different side quests during Chapter 3 – Home Sweet Slum.
Once you have done that you will then be able to unlock the Alone at Last discovery which will play a small scene with just Cloud and Tifa
During this cutscene Tifa will ask you what kind of dress you think she should wear, your choices here reflect what will happen during Chapter 9 – Town that Never Sleeps.
This may require a total of 3 different playthroughs in order to get them all. However doing so will net you the Dressed to the Nines trophy achievement
You will also need to get all of Cloud and Aerith’s different costume dresses too in order to complete the trophy achievement as you are required to get all nine, and each character has 3 different ones to unlock.
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