Bianca is a main character in Pokémon Heroes. She's the granddaughter of Lorenzo and best friends with Latias, a legendary Pokémon with the ability to shapeshift into human form—sometimes as Bianca herself. While Bianca has hair similar to Latias's, she's usually recognizable by her white beret. She's interested in art and observation, with hints that she wants to become a painter or possibly a Pokémon Watcher like Tracey. Most of the time she's friendly and easygoing, though she can turn defensive pretty quickly when provoked.
Bianca first shows up sketching stained glass windows in the local museum. Ash spots her and gets confused because he'd previously saved Latias while it was disguised as a girl, and he thinks Bianca is the same person. He chases her all over Alto Mare trying to figure out why she vanished, but Bianca just thinks he's weird and takes off. Things get more complicated when Ash encounters Latios at a secret garden and the legendary Pokémon attacks him. Bianca arrives mid-fight and immediately assumes Ash is the aggressor, but her grandfather Lorenzo breaks things up and clears the air. Once she realizes Ash isn't a threat, she apologizes and they become friends.
Later, Bianca and Lorenzo get taken hostage in the museum. Bianca manages to signal Latios to use its Sight Sharing ability to bring Ash and Latias to the rescue. They both make it out safely and help stop Latios from being tortured, but the experience leaves Bianca shaken when Latios sacrifices itself. She inherits the Soul Dew afterward.
In the film's ending, Bianca finishes a sketch of Ash and Pikachu and gives it to him—though it's genuinely unclear whether it was actually Bianca or Latias shapeshifted as her. Either way, the girl kissed him before disappearing. She shows up again in the credits, drawing another sketch by the harbor.
Content compiled by AnimeList.moe from publicly available sources.