Once you complete the mission “A Hero’s Duty” You will meet the final faction in the game (Las Catrinas) and be able to get this achievement.
Head - Body Art - Day of the Dead - (Las Catrinas)
Tops - Gloves - Bucky Gloves (Bucky)
Bottoms - Footwear - Samurai (Troop Bushido)
Bottoms - Bottoms - Fargarthian Armored Pants - (Fargarthian)
Tops - Outerwear - Wear - Oxford Backpack - (Oxfords)
I bought Samurai and Fargarthian Armored Pants from the vendor, the rest I already had in customise, after equipping all 5 the achievement popped.