The relationship between Stiles and Lydia was incredibly one-sided at first, as Stiles had developed a crush on Lydia as early as the third grade, but Lydia, who was in a long-term relationship with Jackson Whittemore, didn't notice or acknowledge Stiles' existence until they were sophomores in high school. However, after Peter Hale killed Laura Hale to become an Alpha and subsequently gave the Bite to Stiles' best friendScott McCall, the supernatural world began to affect the lives of Stiles, Lydia, and the rest of their friends, which caused them to start spending more time around each other.
From there, Lydia and Stiles' relationship grew from mere acquaintances through mutual friends to Lydia begrudgingly tolerating Stiles. Things finally started to improve in February of 2011 during their sophomore year, when finally, after Lydia was convinced to attend the Winter Formal as Stiles' date by Lydia's best friend Allison Argent, she began to see Stiles as a nice guy who liked the real her when it became obvious that he was one of the few people who knew that Lydia was actually a literal genius with an IQ of 170. Stiles intervened when Peter attacked Lydia on the lacrosse field and offered himself up to save her life, and after she was hospitalized, he spent the entire weekend sleeping in the lobby to make sure she was okay.
The pair got somewhat closer throughout Season 2, though the fact that Stiles, along with Allison and Scott, wanted to ensure Lydia's safety by keeping her in the dark about the supernatural (combined with the terrifying side-effects Lydia was experiencing on her own as a result of her newly-activated Banshee powers and Peter's spiritual possession of her mind), led Lydia to be ostracized from all of her friends for several months. Fortunately, once Lydia was finally informed of everything that was going on after it was revealed that Jackson, a newly-turned Kanima, had been resurrected by his powers, she and Stiles proved themselves to be an excellent team when they arrived just in time to prevent Jackson from killing everyone.
However, though Stiles and Lydia quickly became close friends after Lydia joined the McCall Pack, their relationship wasn't romantic, although Lydia did kiss Stiles in the middle of Season 3 in order to snap him out of a panic attack. Whether Lydia had genuine romantic feelings for Stiles remained unknown, and Stiles' crush on Lydia seemed to be put on hold while both of them hooked up with and dated other people throughout Season 3, Season 4, and Season 5; Stiles had brief flings with Heather and Caitlin before beginning a romantic relationship with Malia Tate, whereas Lydia had a romantic relationship with Aiden and a flirtatious friendship with Jordan Parrish.
In Memory Lost, Stiles finally admitted to Lydia that he loves her before he was taken by the Ghost Riders and erased from her memory. In Superposition, though Lydia doesn't know who is missing from her life, she informed Scott and Malia that she thought she loved them, indicating that Stiles' earlier confession is reciprocated. In Memory Found, Lydia confessed that she does love him, and that everything changed after she kissed him to stop his panic attack. Upon reuniting in Riders on the Storm, Lydia confessed that she didn't reply after Stiles said "Remember that I love you". However Stiles said she didn't need to say it and the two shared a passionate kiss. After that, Lydia and Stiles run to the exit of the school but stops when Stiles hears his mom saying his name. Lydia explains to Stiles about what happened when he was gone, that the Wild Hunt was tricking him. Stiles's mom tries to attack Stiles but Lydia steps in front him, trying to protect him by using her banshee powers. Stiles's mom stops Lydia from screaming, by grabbing ahold of her throat, which led to Stiles trying to help Lydia and ended up getting choked himself. Sheriff Stilinski (Stiles's dad) comes and tries to shoot Claudia (Stiles's mom) to stop her from killing Stiles. When the bullet didn't kill Claudia, Lydia comes in and tells the Sherrif to, "Fire again." Lydia using her banshee powers and Sherrif Stilinski shooting the bullet, worked as a team to help Stiles from being killed by Claudia. When Stiles and Scott were cleaning out their lockers for the end of the school year, Scott happy and excited that their finally graduating high school, says how it felt like nothing has changed. Stiles looking to Lydia, and Lydia looking back at him, smiling, Stiles tells Scott, "Everything's changed." Later on, Stiles tells Scott that Lydia's driving him down to DC to help him move him into his dorm, and for Scott to take care of his jeep. As of the mid-season final of Season 6, Stiles and Lydia are now in an offical relationship.
Both Lydia and Stiles have proven their dedication to their strong relationship, by doing everything they can, including putting themselves into danger, in order to protect each other. For example, Lydia went to extreme lengths to learn how to use her powers to save Stiles from his possession by the Nogitsune, to the point where she even asked her attacker, Peter Hale, for assistance, while Stiles broke into the closed unit of Eichen House without reliable backup in order to save Lydia from being consumed by her powers after Gabriel Valack performed trephination on her. Lydia also showed herself willing to use her banshee powers to save Stiles after he was attacked by a Ghost Rider, and later on a hallucination of his mother created by the Wild Hunt.
Stiles and Lydia are also known as Stydia, or, less frequently, Martinski, by fans.
In Second Chance at First Line, Stiles ran into Lydia again at Beacon Hills Memorial Hospital while he was acting as a lookout for Scott, who had gone down to the morgue to get the scent of the recently-deceased woman he found in the woods. Stiles once again attempted to talk to Lydia, acknowledging that he knew that they didn't know each other well before stating that he believed they had a connection. However, Lydia soon revealed that she had been talking to someone else on her Bluetooth device for her phone the entire time while Stiles was talking and either didn't hear him or vaguely heard him and simply didn't care. Lydia asked him if it was worth repeating, and Stiles, embarrassed, said no and walked away just as Lydia's then-boyfriendJackson Whittemore walked out of the clinic to leave with her.
In The Tell, Stiles briefly saw Lydia with Jackson outside of 2*C Video Store when he and Sheriff Stilinski came to investigate the recent murder of the video store clerk that Jackson witnessed. However, Lydia was too shaken to interact with Stiles, and Jackson was too intent on leaving the scene to go home for them to spend much time together.
The next day, Stiles, curious to know what Lydia saw when the Alpha fled the scene of his most recent murder at the video store, went to the Martin House to talk to her. Unfortunately for Stiles, Lydia had been given a great deal of anti-anxiety/sedative medications that made her too high to really engage with him. When he asked her what she saw that night, Lydia continued to repeat that she saw a mountain lion, since that was what she was told had run out of the video store. Upon realizing how inebriated Lydia was, Stiles had her try to say a tongue-twister, but she was too high to be able to say it properly. It almost looked as though Lydia wanted to hook up with Stiles, and Stiles seemed willing to do so despite Lydia's intoxicated state until she called him "Jackson," causing Stiles to sigh in defeat and give up. However, when Lydia passed out in his lap, Stiles took a chance and looked through her phone and was shocked to find that she had captured a video of the Alpha running out of the video store and sent it to his own phone before deleting it from hers.
In Lunatic, Stiles, feeling badly for Scott after his break-up with Allison, took him out to the Beacon Hills Preserve with a bottle of Jack Daniels whiskey he stole from his father's liquor cabinet. However, though Stiles got extremely drunk, Scott realized that his werewolf healing prevented him from getting intoxicated whatsoever. Due to Stiles' drunken state, his encouraging pep-talk about Scott and Allison's relationship inevitably turned to Stiles talking about Lydia's strawberry-blonde hair, green eyes, and 5'3" stature.
The next day, when Stiles learned that the impending full moon had heightened Scott's werewolf senses so much that he could smell jealousy, he begged Scott to go ask Lydia if she liked him and use his sense of smell to determine if she did or not. However, Lydia, who had strange unresolved feelings for Scott, started to make out with Scott before they could talk about Stiles, and Scott responded enthusiastically because of the full moon changing his personality. Afterward, Scott lied and told Stiles that Lydia was into him, but after seeing Lydia's perfect pink lip gloss had smeared, he realized that the two had made out and became angry.
Stiles then brought up this make-out session that night after he tricked Scott and handcuffed him to the radiator to prevent him from running loose during the full moon. He acknowledged that the full moon had influenced his behavior but still accused him of being a bad friend before rubbing it in by putting water in a dog bowl labelled "Scott" and laying it on the floor in front of him.
In Formality, after learning that Lydia had made out with Scott, Allison convinced Lydia to go to the winter formal dance with Stiles while she went to the dance with Jackson (who had broken up with Lydia some time earlier) just as friends. However, Lydia did not ask Stiles to the dance on-screen, though Stiles was seen dress-shopping with Allison and Lydia after school that day. While they shopped, Lydia dumped an armful of dresses into Stiles' arms to hold while she continued to browse the store.
That evening, Stiles drove Lydia to the dance, where the two ran into Allison and Jackson in the parking lot of the high school. Jackson was his usual sarcastic and rude self, leading Lydia to become fed up with how he has been treating her. She muttered under her breath that she wasn't going to be like the other neurotic girls who "pull up their skirts at the first flattering remark," but when Stiles overheard her and told her he thought that she looked beautiful, Lydia seemed to really see Stiles for the first time and appeared to relax around him, taking his offered arm and walking into the dance with him.
Despite this slight change of opinion regarding Stiles, she still refused to dance and spent the first part of the night sitting sullenly at the table. When Stiles finally ordered her to get up and dance, Lydia continued to reject him, though she did give him points for his forwardness. It was then that Stiles pointed out that he has had a crush on her since he was in the third grade and that he was probably the only person who knew how smart she really was before adding that one day, she would be accepting the Nobel prize for a mathematical theorum she would create. Lydia, impressed by Stiles' observational skills, corrected him by saying that the Nobel doesn't have prizes for mathematics and that she would instead be winning the Fields Medal before she finally agreed to dance with him, leading Stiles to fist-pump several times in excitement. The two danced together through several songs before Lydia noticed that Jackson was nowhere to be found. Stiles, noticing her concern, didn't fight her as she left to go look for him, but after she had been gone for some time, he went to go looking for her.
In Code Breaker, Stiles saw Lydia being attacked on the lacrosse field by Peter Hale and immediately rushed toward her to try to save her, even offering himself up to be killed in her place. However, Lydia had already been bitten by Peter, who had been revealed to be the Alpha several episodes earlier, and Peter would only agree to leave Lydia as she was if he came with her, forcing Stiles to call Jackson to have him rush her to the hospital while Peter used him to find Scott so they could find Derek together.
At the end of the episode, after Peter had been killed and everything was taken care of, Scott and Stiles returned to the hospital where Lydia had finally pulled through the worst of her injuries. However, when Scott lifted up her bandages, expecting to see her wounds healed in the process of Lydia becoming a werewolf, since she hadn't died from the Bite, he was shocked to see that her bite and scratch wounds were still there, albeit healing at a slow human pace. Confused, they discuss what this could mean for Lydia, since the Bite is meant to either kill or turn a human, and the fact that neither happened to Lydia seemed to indicate that she wasn't turning into a werewolf.
In Omega, Stiles was seen spending the entire weekend in the waiting room outside of Lydia's room at Beacon Hills Memorial Hospital for moral support, where he was sprawled out across three wooden lobby chairs, where he seemed to be having some very naughty dreams about Lydia. In her room, Lydia declined her father's assistance in taking a shower while Stiles went to the vending machine for snacks. Lydia heard the smashing noise caused by Stiles' attempt to shake his stuck candy bar, which had led to him accidentally knocking the machine over onto the floor. However, she ignored the sound in favor of continuing her shower.
She suddenly noticed the water near the drain turning black, which led her to kneel down and reach for what could be causing it. She first began pulling out large handfuls of tangled dark hair before a burned hand reached out of the drain and grabbed her by the wrist, causing her to scream at the top of her lungs. Stiles instantly heard the scream, recognized that it was Lydia, and rushed into her room, shoving past her father and Melissa McCall to see if she was okay. However, she was nowhere to be seen, and the water was perfectly clear, indicating that Lydia had been hallucinating the hand and the dark water. They then noticed that the window was wide open, suggesting that Lydia had jumped out of the room, leaving her hospital gown behind.
Stiles, desperate to find Lydia, snagged her hospital gown from her room and rushed it over to Scott so that he could use it to get her scent and track her down. Scott and Stiles were then joined by Allison, who informed them that her father and several fellow Hunters left in SUVs, presumably to track Lydia, who they believed had been transformed into a Werewolf as a result of Peter Hale's Bite. Stiles worried aloud for Lydia's safety, and Scott assured him that they wouldn't let anyone hurt her again. Using Lydia's scent, they first tracked her to the Hale House, though she was nowhere to be found. They then tracked the scent trail to a nearby ambulance, where a body had been brutally ripped apart inside, leading Stiles to wonder if perhaps Lydia really had become a Werewolf. Stiles eventually caught up with his father, Sheriff Stilinski, and the two ultimately were able to find the naked Lydia coming out of the woods, looking incredibly disheveled from spending over a day running through the wild in a trance. Stiles rushed to try to peel Sheriff's jacket off of her to help cover Lydia up, but in his haste, he tripped over his own feet and fell onto the ground.
In Ice Pick, Stils and Lydia were in gym class with Scott, Allison, Jackson, and Erica Reyes, with Coach Finstock as their teacher. Coach sent pairs of students to climb up the rock wall in the gym, and Erica and Stiles were sent up together; Stiles was able to easily scale the wall and return to the floor without incident, but Erica, a shy and timid loner, began to panic halfway up and was frozen in fear, unable to force herself to go any higher and still too scared and embarrassed to come down, either. Stiles joined Lydia, Scott, and Allison on the ground, where Coach assumed that Erica was suffering from vertigo, causing Lydia to point out that vertigo is a vestibular disorder of the inner ear, and that Erica, in her words, was "just freaking out."
In Abomination, Lydia, who was still suffering from the after-effects of her attack (including sleepwalking continuing to have strange and terrifying hallucinations regarding Peter Hale) and who had been viciously yelled at by Jackson earlier in the day due to his mistaken belief that she had somehow made him immune to Derek Hale's Bite and thus unable to transform into a Werewolf, Lydia went into her car and began sobbing angrily. Stiles, who had been sitting on the bench during their lacrosse game, was tasked with breaking into Gerard Argent's office to steal the Bestiary, which they mistakenly believed was there, by Scott and Allison, in hopes of figuring out what the new shapeshifter was.
On his way there, he came upon Lydia and went to talk to her, despite Lydia's protests that she wanted him to go away. When he asked her what was wrong, she once again demanded that he leave because the last person she needed was someone to see her cry. Stiles insisted that she, of all people, shouldn't care whether people saw her cry or not because of how beautiful she looks when she's crying. Lydia, starting to slightly trust Stiles, remarked that he was going to think that she is crazy, but Stiles, knowing full well how unbelievable the supernatural world could be, assured her that there was literally nothing she could say that would make him think she was crazy.
However, Stiles, hearing the whistle being blown in the game and realizing he was running out of time to sneak into Gerard's office, groaned regretfully and asked her if she could wait five minutes, assuring her that he would be right back and she could then tell him everything. Unfortunately for them both, Stiles was then confronted by Derek and Erica inside, where they were then attacked by the mysterious shapeshifter that was later revealed to be a Kanima, preventing Stiles from catching up with Lydia.
In Restraint, Scott, Stiles, and Allison are trying to figure out what happened in Jackson’s past that made him turn into a Kanima instead of a werewolf when he was bit. Stiles realizes that Lydia probably knows so he tries asking her about it.
In Party Guessed, at Lydia's party, Lydia is less than surprised at Stiles usual tactics of impressing her. And she is hoping for someone less predictable to show up this evening.
In Battlefield, Lydia attended the lacrosse game with Sheriff Stilinski and Melisa McCall. Due to the fact that Scott was barred from playing by Gerard Argent due to poor grades, and multiple players were injured in the game, Coach had no choice but to put Stiles in the game. Stiles was predictably bad at first, but after he heard Lydia cheering for him in the stands, he managed to get the confidence necessary to make his first goal. Motivated by Lydia's support, he was able to make several more goals, allowing the team to win the game despite being the underdogs.