Nintendo Japan has revealed the new Nintendo 3DS themes and Pokémon Pikachu's Voice! (ポケモン ボイスつき!ピカチュウト) and Pokémon Dancing Pikachu (ポケモン ピカチュウダンシング!) were announced. These themes cost 200yen and 250yen each and are available for purchase from August 19th, 2015 until September 30th, 2015 on the Nintendo 3DS eShop store.

Pokémon Pikachu's Voice! (ポケモン ボイスつき!ピカチュウト)

Features: Pikachu's in a colorful theme with a large picture of Pikachu's face on the top screen. Pikachu's voice also plays during user actions such as when sleep mode is canceled, sliding the screen or starting software.
Music: XY - Route 1 (~1番道路~)

Pokémon Dancing Pikachu (ポケモン ピカチュウダンシング!)

Features: A bunch of Pikachu's dancing on a stage.
Music: Pikachu Dance (カチュウダンス)

Sources: and