The Pokémon anime has long enjoyed shaking up its cast of regulars, changing out Ash's Pokémon companions as he travels to new lands and meets new people. That fact has often been controversial with fans, though, as it meant beloved characters were leaving and being replaced by unfamiliar new ones, which can lead to disparaging remarks about the new characters. Dawn, however, managed to set herself apart by one particular incident.
Dawn joined the Pokémon anime when Ash hit the Sinnoh region around 2007. At the time, she was only Ash's third female companion, following Misty (from Pokémon's Kanto and Johto eras) and May (from the Hoenn era). Both Misty and May had been around for quite a long time, and had many fans. Both also had slightly antagonistic relationships with Ash, where they would bicker over unimportant things constantly. As Ash has gradually matured though, that aspect of his relationship with his female friends has diminished, and all of that started with Dawn.
Dawn is Ash's Most Easy-Going Pokémon Companion
While Ash and Dawn certainly had disagreements over their time together in the anime, the bickering was already being turned down. Much of the antagonistic elements of Ash's relationship to Misty began with how they met--Ash "borrowed" her bike and destroyed it in the process with Pikachu's Thunder Shock. Misty's excuse for traveling with Ash from that point forward was simply that she wanted him to pay her back for destroying her bike, and he actually did replace it eventually. This means of meeting girls turned into a bit of a running joke in the anime, as Ash similarly destroyed May's bike upon arriving in Hoenn, and she was equally upset about it. When the same thing happened to Dawn, though, events played out very differently.
In the second episode of the Diamond and Pearl anime season, entitled "Two Degrees of Separation," Pikachu once again accidentally destroys a bike, this time using Thunderbolt when Dawn mistook it for a wild Pikachu and attacked. She soon discovered Pikachu belonged to Ash, and returning it is what facilitated their meeting. What this really meant, though, was that Ash had no idea that Pikachu had destroyed a bike this time. And much to Dawn's credit, she doesn't immediately start yelling at him about the bike when they meet. In fact, Dawn doesn't even mention it until "One Big Happiny Family," 36 episodes later, and is willing to let it go and forgive Pikachu (and Ash). This showed fairly quickly that Dawn wasn't going to be the same type of companion as Misty or May, even if she was technically filling their shoes now.
While it might seem like a fairly small detail, it's a deliberate one that proves Pokémon was trying to ensure Dawn had a distinct character, something that ultimately succeeded since Dawn's role in the series evolved in a very different way.