Aiden: "It's okay. Lydia never believed I was one of the good guys, anyway."
Derek: "She'll believe me."
Aiden Steiner's last words about Lydia in The Divine Move

The relationship between Omega Werewolf Aiden Steiner and Banshee Lydia Martin

Aiden and Lydia's relationship began shortly after Aiden's introduction in Season 3A's Tattoo when they saw each other at school. Immediately attracted to him on a physical level, Lydia sought Aiden out at school and the two began engaging in a friends-with-benefits-style relationship. This relationship grew stronger over time until Lydia learned that Aiden and his twin brother Ethan were actually adult Alpha Werewolves with the power to merge themselves into an extra-large Werewolf and who were members of the Alpha Pack, which had been terrorizing Derek Hale, Scott McCall, and the Beacon Hills packs in an effort to recruit the former two to their ranks.

However, it was shown that Aiden's loyalties had changed when he growled at his packmate Kali when she threatened Lydia's life, and he and Ethan's merged neck was snapped while defending Lydia from the Darach Jennifer Blake. Aiden and Lydia then had a brief break in their relationship after the injuries the twins sustained caused them to revert back to Omegas, though Lydia was the only one of the McCall Pack members who stayed in contact with them.

Aiden then got the idea to try to join the pack in hopes of becoming a Beta and having the strength necessary to defend himself from the people he and Ethan "pissed off" when they were Alphas, and he was angered when Scott said no as a result of his part in Vernon Boyd and Erica Reyes' deaths. When Ethan reminded him that the best way to get the pack to reconsider was to do something nice, Aiden began trying to win Lydia back over, even after she informed him that she had recently helped save someone's life and that she wanted to be with a good guy, not with a bad guy.

Despite Lydia's comments, Aiden helped save her life after she was thrust into a hypothermic state after she was scanned by the Oni to ensure that she wasn't possessed by the Nogitsune, and their relationship was rekindled after Aiden and Ethan helped defend Lydia's close friends Scott McCall and Kira Yukimura from the Oni. Their relationship continued until the end of Season 3B when Aiden was fatally stabbed in the chest by an Oni. As he died, Aiden expressed regret that Lydia still thought he was one of the bad guys, but Derek Hale assured him that he would make sure she knew that he was the opposite. Lydia's Banshee instincts caused her to sense Aiden's death, and she was visibly upset when she ran outside and saw Ethan, Derek, and Chris Argent congregated around his body.

In Season 5, Gabriel Valack used his Illusion Casting power to make himself look like Aiden in an effort to prevent her from leaving Eichen House before he could use her powers to figure out who the Beast of Gevaudan was.

Aiden and Lydia are also known as Laiden by fans

Throughout Teen Wolf

 In Tattoo, Lydia Martin and Allison Argent were talking in the hallways of Beacon Hills High School about Lydia's intent to find a boy with whom to distract herself when suddenly, Aiden and his twin Ethan entered the hall with their motorcycle helmets, immediately catching the girls' notice, though they did not interact with the new students.

In Chaos Rising, while Allison and Lydia were studying the symbol bruised into their arms by Braeden in the high school library when they saw Aiden and Ethan enter the library and bump into Danny Mahealani. Lydia leered at them and remarked that she wanted one, and when Allison smirked and asked her which one, Lydia gave her a look and retorted, "The straight one, obviously." When Allison turned around to follow Lydia's gaze, she realized that Aiden's twin brother Ethan was clearly interested in Danny, who looked flustered by the fact that he literally ran into him. Allison turned back around to find that Lydia had fled her seat in order to talk to Aiden herself.

In Frayed, Lydia and Allison were driving behind the school bus carrying the entire Beacon Hills High School cross-country team (which included Scott McCall, Stiles Stilinski, Isaac Lahey, Vernon Boyd, Danny Mahealani, and Ethan Steiner) to their meet. Upon seeing that Allison's car was almost out of gas, the two debated stopping, with Allison wanting to keep following the bus while and Lydia arguing that they should stop to fill the gas tank, as they knew where the team was headed and could catch up later.

When Allison pointed out that she didn't see what happened during the battle at the Abandoned Mall between Scott and the Hale Pack against the Alpha Pack, Lydia quietly muttered that she knew who started it. Allison, taken aback by this answer, asked if that was what Aiden had told her, Lydia realized that Allison had invited her on this "road trip" so that she could both keep an eye on the pack, the twins, and Lydia. Allison turned the subject back to Aiden and Lydia and asked if there really wasn't anything going on between them, Lydia rolled her eyes and applied her lipstick in the flip-down mirror, stating that she was appalled by the insinuation that they were in a relationship.

However, the flashbacks to several days earlier told a different story. In the flashback, Aiden and Lydia had sneaked into Coach Finstock's office, where they began making out. After a moment, Lydia pulled away and gave Aiden a look before asking him what he thought he was doing. When Aiden asked her what she meant, Lydia pointed out his hands, which Aiden assured her were on her waist. Lydia sarcastically retorted, "I know. What am I, a nun? Put them somewhere useful." This amused Aiden so much that his hands traveled down to the back of her upper thighs before picking her up and wrapping her legs around his waist as he continued to kiss her. A few moments later, Aiden smirked and asked Lydia if that was better, and Lydia smugly replied, "Moderately" before the two picked back up again.

In Currents, Ethan admits that he and his brother went after Lydia and Danny because they knew one of the two would be important to Scott. Aiden and Lydia make out.

In The Girl Who Knew Too Much, Aiden is seen making out with Lydia until she confronts him about killing Boyd.

In Galvanize, after Aiden's comeback, he and Lydia make out in an office.

In Illuminated, Aiden sets up a Halloween Party for Danny, trying to prove to Lydia that he is not a "bad guy". When Aiden and Danny search for Ethan at the party, he sees Lydia lying on the ground by attacking by the Oni.

In Riddled, Aiden helps Lydia search for Stiles. He tells Derek of Stiles suspicions that he helped Barrow.

In Insatiable, when Ethan and Aiden are trying to find Lydia, they are shot at with bullets laced with wolfbane and are both hit several times. They are saved by Derek.

In The Divine Move, when Aiden is killed by the Oni, Lydia felt his death and cried at Stiles Stilinski's shoulder.

Gabriel Valack used his Illusion Casting powers to appear as Aiden when Lydia attempted to escape from Eichen House, where he informed Lydia that she couldn't leave yet because her treatment wasn't done. Valack continued to masquerade as Aiden until Lydia realized that he wasn't real, after which point he returned to his usual appearance in order to continue to question her about the events that occurred before she was admitted.