From Bulbapedia, the community-driven Pokémon encyclopedia.
Flames surround a pitch-black area. Wicked lightning bolts strike a dark sky. In the flames, a Reshiram appears; in the lightning, a Zekrom appears. They begin to speak...
According to Zekrom, a disaster will strike-a disaster so huge that it will swallow up the two worlds. Still, with Reshiram's and Zekrom's immense power, they might be able to stop it. And even if all is meant to be demolished, there is still hope. Suddenly, Reshiram notices a light...not from the coming disaster...still, the light is hardly visible. The light seems to be a creature, a "he", but is he able to stop the disaster? More lights are still forming, making blinding brightness, until it's too much to take...
A Pikachu is running in a tunnel. It stops, however, once it hears the call of its longtime friend, Piplup. Quickly running towards each other, they greet each other happily.
You are soon playing as Pikachu, so go up to Piplup. Holding the Wii remote horizontally (this applies for all controls), press the "up" button to walk towards Piplup. Once you're near Piplup, press 2 to talk to him. You'll learn that he went to Seasong Beach the other day, and wants you to go with him.
Follow Piplup. You can simply walk, but to make it quicker, press 1 repeatedly to Dash. Dashing is needed in the next stage of the game-Piplup stops leading you to Seasong Beach because he noticed a strange box. After dashing into it and collecting the berry (after all, berries are "berry" useful), Piplup will start leading you again to the beach.
Piplup has clambered up the steps, and expects you to do the same. Press 2 to jump and reach him.
Chase has returned from its prequel, and it's basically the same concept-as always you will be chasing the Pokémon instead of being the one being chased. Piplup challenges you to a chase, claiming that the tunnel is the perfect spot. Once you Dash into your opponent, you win the berry useful berries. The opponent will also become your friend.
Piplup isn't very fast, so it's relatively easy to knock into him--take note that not all Pokémon will be this slow and easy to beat.
After beating him, Piplup will give you the PokéPark Pad. Here, you record the friends you make and save your progress. Piplup will want you to open your PokéPark Pad-to do so press +.
Piplup will lead you through the tunnel again. It's not long, however, before you are stopped yet again-a Timburr interrupts you and Piplup. Since he is training, he wants you to hit him with your strongest move (Thunderbolt. To hit him with Thunderbolt, press and hold 1 to charge up. Release once electricity is fully charged up. To hit the desired target, press B to change the direction Pikachu is facing.
After getting shocked, Timburr (unconvincingly) says that it didn't hurt at all. Since he has a feeling that you have doubts, he challenges you to a battle.
Battling returned from its prequel. To use moves, you can use Tackle (by Dashing into the opponent) or Thunderbolt, and later, you can use Iron Tail. Pressing 1 repeatedly on the foe will make you do a combo. You win if you manage to drain all of the opponent's HP; you lose if they manage to drain all of your HP. The gauges on the screen indicate how much HP you have left.
After you defeat him, Timburr will admit that your Thunderbolt caused him pain from the start. He likes you, and soon he befriends you.