At the young age of 10 years Dawn, also known as Hikari in Japan, was already training Pokémon in the town of Twinleaf, which is located in Sinnoh. At one point in time, Dawn's mother Johanna was a great Pokémon coordinator that once one the Grand Festival. So, wanting to be just like her mother, Dawn put all her effort into becoming a Pokémon coordinator as well.
The first Pokémon that Dawn Hikari trained was a Piplup. Professor Rowan had given Piplup to her as a gift. Now, Dawn had specifically chosen Piplup as her first starter Pokémon, because they had a little bit of history together. They had already gone on an adventure of there own, together.
Once upon a time, Dawn ran into an injured Pikachu which she tried to capture because she thought it was a wild Pokémon. But, it just so happened that this Pikachu happened to belong to Ash Ketchum who was Pikachu's traner. So, Dawn and Piplup are now travelling Ash and Brock through the land of Sinnoh, encountering many adventures along the way.
Dawn Hikari's first Pokémon are Piplup, Buneary which was the first Pokemon she actually captured, Pachirisu and Buizel.