Piplup is Dawn's first Pokémon that she received from Professor Rowan. It has quite a stubborn attitude and it always thinks it is right.

On the way to Sunyshore City

In a meadow en route to Sunyshore City, during Ash's Gible's training session, Dawn's Piplup constantly got hit by its unsuccessful Draco Meteor attacks. After it had enough, it started yelling at Gible and when the Land Shark Pokémon ignored it, Piplup unleashed numerous BubbleBeam and Whirlpool attacks on it. Seeing as the group didn't seem to care for it, though, Dawn's Piplup wandered off into the nearby forest by itself.

It later encountered Team Rocket disguised as members of an organization called the Pokémon Rescue Corps, who promised to help Dawn's Piplup by talking to the Trainers at fault. After they let Ash and Dawn know how Piplup felt, the Penguin Pokémon was really grateful for what they did. In order to show its gratitude, it agreed to bring Pikachu to them, as it fell for their excuse that they just wanted to ask Pikachu if there's something troubling it as well. Dawn's Piplup led Pikachu to them, but Team Rocket deceived the Pokémon and trapped them into a cage. However, due to a stray Rhyperior's attack, Dawn's Piplup and Pikachu managed to break free from Team Rocket's trap and were reunited with their Trainers. Then, Ash and Dawn, as well as Ash's Gible, apologized to Piplup.

Later on, during the battle with Team Rocket, Dawn's Piplup got really angry after being attacked by James's Carnivine's Vine Whip and it learned a new attack, Hydro Pump, which it unleashed on the evil team and sent them blasting off.

Ash's Oshawott and Dawn's Piplup Rivalry

Ash's Oshawott and Dawn's Piplup both fell in love with Meloetta and the two of them began a rivalry to win the affection of Meloetta. Ash's Oshawott would often come out of its PokéBall when it could tell that Dawn's Piplup was trying to take advantage of a situation. Even though the two of them often argued, they found a common ground and became friends after Meloetta left.

Pokémon World Tournament Junior Cup

Dawn's Piplup participated in the Pokémon World Tournament Junior Cup at the Kagome Town stadium. In the first round it was in the seventh match and faced off against Ramone's Stoutland. The match quickly showcased Dawn's Piplup finishing off Ramone's Stoutland to win the battle which allowed Dawn to advance to the second round while Ramone was eliminated from the tournament.