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Allison and Lydia first met in Season 1's Wolf Moon, and from the on, they were practically inseparable. Their friendship quickly grew to a close, almost sisterly relationship that was very similar to the brotherly relationship between Scott and Stiles. In the first season, Lydia helped Allison adapt to being in a new school and navigate her relationship with Scott McCall. After Lydia was attacked by Peter Hale in Formality, Allison was so distraught and concerned about Lydia's injuries and possible transformation into a werewolf that she was more easily manipulated by her aunt Kate into attacking Scott and Derek Hale.
Throughout Season 2, Allison tried her best to keep Lydia safe by keeping her in the dark about the supernatural, which was ultimately detrimental to Lydia's well-being, since Peter's attack had triggered her latent Banshee abilities and she was struggling to understand what was happening to her. Though Allison tried to support Lydia as best as she could while keeping the secret of the world of werewolves from her, Allison herself would eventually admit that Lydia's mental instability due to Peter's spiritual possession of her mind and her burgeoning Banshee powers were made worse by the fact that she, Scott, and Stiles had ignored her, making it the low point in the girls' relationship.
However, by the beginning of Season 3, Allison and Lydia's close friendship became stronger than ever, due in part to the fact that they were both single, as Allison and Scott had broken up at the end of the previous season, and Lydia and Jackson had also broken up after Jackson Whittemore moved to London. Allison dedicated herself to being a better friend to Lydia after the previous mistakes she had made, supporting Lydia as her Banshee powers continued to grow, and in turn, Lydia also helped support Allison after the loss of her mother. The two worked together to help figure out the plans of the Darach, the Alpha Pack, the Oni, and the Nogitsune in turn while they became more and more loyal to the McCall Pack.
Things made a turn for the worse in De-Void and Insatiable after Lydia was captured by the Nogitsune and brought to Camp Oak Creek. Lydia had experienced a Banshee premonition of Allison's death just prior to her abduction and left several messages behind to try to keep Allison and the pack from coming to find her, as she knew Allison would meet her end if she came to the battle. However, Allison was determined to ensure the survival of her best friend and went to Oak Creek with Scott, Stiles, Kira, and Allison's boyfriend Isaac.
While Scott and Stiles went to save Lydia in the tunnels under Oak Creek, Allison, Isaac, and Kira stayed behind, where they were forced to engage in battle with the Oni, who had been hijacked by the Nogitsune. Though Allison managed to outright kill an Oni with her homemade silver arrowhead, a feat thought to be impossible for all but only the most powerful supernatural creatures, another Oni stabbed her through the abdomen before they disappeared. Allison fell into Scott's arms as she died, and her last words began with her desperately asking if Lydia was alive and safe. Meanwhile, in the tunnels, Lydia felt Allison's death and wailed a heartbreaking Banshee scream in response.
Though Allison is no longer physically with her, Lydia continues to both mourn Allison's death and honor her life by never letting go of her memory. She even learned how to fight like Allison did, and when Stiles mentioned that Allison would have been with them through their senior year if she could, Lydia firmly insisted that she was still there with them.
Allison and Lydia are also known as Allydia by fans.
Throughout Teen Wolf
In Wolf Moon,
In Pack Mentality,
In Magic Bullet,
In The Tell,
In Heart Monitor,
In Night School,
In Wolf's Bane,
In Code Breaker,
In Shape Shifted,
In Ice Pick,
In Party Guessed,
In Master Plan,
In Chaos Rising,
In Motel California,
In The Overlooked,
In Alpha Pact,
In Lunar Ellipse,
In The Dark Moon, Araya Calavera brought up the symbolism of "the dark moon," namely the fact that it was meant to reflect on grief and loss, while in a conversation with Stiles and Lydia, implying that she knew of Allison's death and how close Allison and Lydia were. The reminder of Allison's death made Lydia teary-eyed and more determined to get Derek Hale back from captivity to ensure she didn't lose another pack member like she did Allison.
Lydia mentioned Allison again while she, Stiles, Scott, Kira, and Malia were on their way to La Iglesia with Braeden, as they were discussing Kate Argent and her recent resurrection. She explained that Kate was Allison's aunt and a complete psychopath, likely remembering how Kate had tried to corrupt Allison in Season 1 in addition to the fact that Kate set the Hale House Fire.
In The Benefactor, Lydia was stunned when she received a Banshee premonition while in the study at the Martin Lake House which revealed that the first cipher key to the Deadpool hit-list was "Allison," the first of three names of McCall Pack members who had died or were going to die whose names unlocked the three portions of the list.
In Creatures of the Night, Lydia watched as Scott wrote the initials "A.A." next to his own on the bookshelf at Senior Scribe. When Stiles stated, "Allison would have been with us" after he, Lydia, Scott, Kira, and Malia finished writing their initials, Lydia smiled weakly and replied, "She still is."
In Apotheosis, Stiles and Lydia discussed Allison in the aftermath of the battle with Sebastien Valet, also known as the Beast of Gevaudan. Stiles told her the story of how Sebastien accidentally performed the werewolf memory manipulation ritual when he impaled his claws into Scott's spine, causing him to Scott's memories; since Scott believed he was about to die, his mind flooded with memories of Allison, including his memory of Allison and Lydia practicing archery in the woods in Anchors, and since Allison resembled Sebastien's sister and the original Argent matriarch Marie-Jeanne Valet, Sebastien became so shocked that he let go of Scott. Lydia realized this meant that Allison and Marie-Jeanne must have resembled each other, and possibly looked exactly alike, and when Stiles pointed out that Allison once again saved Scott's life, Lydia smiled proudly with tears in her eyes.
- Both Lydia and Allison have made out with Scott McCall, though Lydia only did it once as a sort of power-play in Season 1 when she was still more of a mean-girl, while Allison was in a relationship with Scott for several months.
- In an interesting twist, Lydia showed Derek Hale, Jordan Parrish, and Scott McCall a picture of her grandmother, Lorraine Martin and Lorraine's wife, Maddy, in Season 4's Perishable, in which Lorraine and Maddy closely resembled Lydia and Allison; Lorraine was a redhead with green eyes like her granddaughter Lydia, whereas Maddy was a pale girl with dark brunette hair like Allison. It is possible that this was intended to be a parallel to Allison and Lydia's relationship.
- Allison and Lydia's actresses, Crystal Reed and Holland Roden, are close friends in real life just like their characters on the show.