Because I got a couple, I have my own BoA single but that's more or less all I saw... And I know that there are some - like Miku - which a DLC. Anyway, could anybody make a list with all the requirements for the costume titles? Please :D
Beach costumes Go to -367.196 : -159.583 and see the event. Asbel's swimsuit is in a pot in the desert port town, Ore Reiyu or something like that... I forget...
Cheria's - in Seible Izolle, the middle desert town, you'll need to purchase it for 100,000gald. Check the counter behind the item shop man.
Hubert's - inside Rockgaggan, find a watermelon enemy and beat it down.
Sophie's - in the Strata Cryas ruins, you'll need to defeat an enemy along the path west from the savepoint.
Malik's - speak to the guard at the entrance
Pascal's - In Strata underground ruins, defeat the enemy just above the savepoint. The ruins is southeast of Ore Reiyu.
Formals Asbel's formal - Go pick up an item in that one area/dungeon where Lambda appeared during the kid segment. Go back to Lhant mansion, speak to maid, select the request.
Sophie - Search X334.633 : Y180.499 on the world map. Enter and speak with middle Kamenin.
Hubert - You'll need an item behind the Strata Cryas. Go to the Neko ... place and fulfill the request, just like you would at any other town inn/Asbel's maid. Might need to go to X332.000 : Y -392.000.
Cheria - You'll need an item from Baronia castle. Neko, request.
Malik - At the end of Bashis military base, the crazy box dungeon on the other planet.
Pascal - Supposedly in the same area as her swimsuit, I got it without even realizing...
The DLC costumes available at the moment are Miku Sophie, Idolmaster girls, Guys in suits. Vesperia costumes are preorder bonuses, not sure if they're on dlc shop.