Start a new game, then load a completed saved game file from Xenosaga: Episode 2 on your memory card to begin with Shion's Vector costume from Xenosaga: Episode 2.
Successfully complete the game and save when prompted. Load the cleared saved game file to unlock the Allen Swimsuit and Chaos Flawless costumes.
Successfully complete the Advanced Hakox levels to unlock Ziggy Swimsuit costume.
Successfully complete the game to unlock Swimsuit mode under the "Memory Code" event viewer.
On the south eastern part of the map of Miltia is a small, barely visible side street heading south off the main street. Pass through that street and go to the east to find a treasure chest containing an armor for JR that changes his character model.
In the center of Miltia City is a long west-to-east walkway, with the eastern end turning into another part of the city. There should be a breakable short red gate blocking a building. Destroy the gate and the door to enter the building. Climb the stairs to see a little girl talking about a cat who stole her balloon. The cat is walking back and forth along a horizontal flagpole. Use a trap to make the cat drop the balloon. Then, catch the balloon with Circle for two Berry Ice Creams (Medium HP restore).
Once you are able to move around in Miltia's map, go to the right as far as possible. You will see a treasure chest on top of a building. When you select this chest, text will appear asking for a code. The code is "5150".