From Bulbapedia, the community-driven Pokémon encyclopedia.
The Fashion Case (Japanese: アクセサリーいれ Accessory Container) is a key item in Pokémon Diamond and Pearl as well as Pokémon HeartGold and SoulSilver which holds accessories and backdrops. It can be picked up in Jubilife City after double battling with Lucas/Dawn, with one backdrop and a few accessories to start with. Extra Accessories and Backdrops can be picked up by Pokémon in Amity Square or won in the Pokémon Lottery or a Super Contest. Accessories may also be found by the Massage Lady in Veilstone City or traded from berries at the Pick a Peck of Colors Flower Shop in Floaroma Town. There is also a lady in the Pal Park building who will give the player certain accessories or backgrounds if certain Pokémon GBA games are in the DS's GBA slot. There are several different sections: The fluffs section, the mineral/rock section, the scales section, the feather section, the leaf/beard section, the silver section, the element section, the metal section, the other section, the contest prize section, and the head accessories section. There are fifteen backdrops to collect.