Allison "Allie" Underhill and Ray have been best friends since grade school. Smart and sure of herself, she fits in with everyone at school and gets whatever she needs from her wealthy dad—but she’s not spoiled. She's drawn to the mysterious creatures of the Darkness Civilization and quickly gets attached to them ... which is a strength and a weakness.
Even though her dad is wealthy, Allie does not have the stereotypical "rich girl attitude". Instead she's fiercely independent and incredibly adventurous. She's also very caring, though her selfish side emerges when things don't go her way. As a duelist, Allie quickly becomes emotionally attached to her creatures especially in her bond with Squeaky from the mysterious Darkness Civilization.
Allie is sassy, quick-witted, and self-assured. She fits in comfortably with all the cliques at school from the cheerleaders to the glee club. One thing that Allie and Ray bond over is their love of animals whether they're real or imaginary. She'd punch you out if you stepped on a spider, though oddly enough she's repulsed by touching them. Allie will learn that, in battle, she quickly becomes emotionally attached to her creatures. Her methods will alternately make her a defensive, timid duelist or wildly aggressive with her creatures at her side; it's both her strength and her weakness.
She's not about order but about passion and her being accustomed to getting what she wants means that her selfish side has been nurtured. Mind you, that is not to say in any way that Allie has an evil bone in her body. In fact, because Allie is drawn to the Darkness Civilization, she's proof that no civilization is either good or evil. Her "dark side", if you want to call it that, is enamored by the creepy-cool Tim Burton sensibility of the Darkness Civilization, and this fascination will play a huge part in her choosing Squeaky as her "bestie" in battle.
It can be seen in Duel Hard when Allie's father went into the Darkness Civilization and she tried all that she could to get him back. She got a different attire when she was Megaria's student. When Allie duels in the Darkness Civilization, her mana becomes stronger, which also makes her more susceptible to its influence. In the episode Darkness on the Edge of Town, Megaria tells her she has a natural connection to Darkness, as if she were "born to it".
Allie and Ray have been best friends since early childhood. They connected over both being raised in single parent homes.
As a friend of Ray, she has appeared in (almost) all episodes .