Nathalie Sancoeur is the assistant of Gabriel Agreste. She is in charge of taking care of various tasks for him as well as taking care of his son, Adrien. In the Season 2 premiere, it is revealed that she is aware that Gabriel is Hawk Moth and in the Season 2 finale, she uses the Peacock Miraculous to become the villain Mayura.
In "Ladybug & Cat Noir (Origins - Part 1)", as Adrien attempts to enter Collège Françoise Dupont, Nathalie along with Adrien's bodyguard stop him, reminding him that his father doesn't want him going to school, though Adrien insists that's what he wants. When Adrien spots Master Fu tripped and unable to reach his cane, he runs to help him, therefore allowing Nathalie and the bodyguard to block the steps leading into the building and take him back home. Later, Nathalie, while homeschooling Adrien, quizzes him on history until Gabriel interrupts and firmly tells Adrien that he will not be going to school before exiting. Nathalie offers to end the homeschooling for the day, though Adrien sadly runs up to his room before she can finish.
In "Stoneheart (Origins - Part 2)", Nathalie notices that Adrien is not in his room and informs Gabriel, who scolds her and the bodyguard for failing to notice Adrien leave. Just as Adrien is about to enter the school, Nathalie begs him not to as his father will be furious, though Adrien tells her to tell him that she came too late and enters. Nathalie tells the bodyguard she'll handle it. The next day, per request by Nathalie, Gabriel allows Adrien to continue going to school, to which Adrien thanks both her and his father.
In "The Bubbler", after giving Adrien his schedule, Adrien asks her if his father approved his request for a birthday party, to which Nathalie informs him that he didn't and wishes a saddened Adrien a happy birthday. Later, Nathalie answers the doorbell when Marinette comes over to the Agreste mansion to deliver her birthday gift to Adrien, telling her to put it in the mailbox. Gabriel asks her through an intercom who was there, to which Nathalie tells him that it was a friend of Adrien's delivering him a birthday gift. Gabriel therefore asks Nathalie if she got Adrien a gift on his behalf. Nathalie nervously claims that Gabriel never asked her to do that, though Gabriel yells at her that he did. Nathalie agrees to get it done, and after Gabriel hangs up, she decides to pass off Marinette's gift as Gabriel's. Then Nino comes by and Nathalie witnesses him requesting that Gabriel allow Adrien to have a birthday party and Gabriel's cold refusal. After Nino is akumatized into Bubbler, Nathalie is one of the many adults seen floating in bubbles in the sky. After Bubbler's defeat, Gabriel asks Nathalie if Adrien liked his gift, to which Nathalie says that she'll check. She then approaches Adrien and hands him Marinette's gift, claiming that it's a birthday present from his father.
In "Mr. Pigeon", during Gabriel Agreste's derby hat competition, Nathalie introduces herself to Mr. Damocles and presents Gabriel, who is judging the competition via video chat on her tablet. She takes Gabriel around as he observes all the hats and eventually declares Marinette the winner.
In "The Mime", Nathalie is sitting next to Adrien in the backseat of the Agreste car as they head to the premiere of The Mime's Extraordinary Adventures. She receives a phone call from Gabriel informing her that he will not be able to make it to the show. After hanging up, Adrien asks her if his father is flaking, to which Nathalie says yes but also informs him that his father reserved front row seats. Then Ladybug shows up as she battles Mime and tells everyone in the car to get out and find a safe hiding spot. Nathalie is then seen running away along with the bodyguard.
In "Volpina", after Adrien snoops into his father's safe, Nathalie enters the atelier and alerts Adrien that he'll be late for school.
In "Santa Claws", Nathalie and Adrien are decorating a tree for Christmas when Adrien asks if his father is coming. Nathalie suggests that they give him a few minutes, though Adrien believes that his father won't come and sadly heads to his room. Therefore, Nathalie approaches Gabriel in his atelier and reminds him that it's Adrien's first Christmas without his mother. Gabriel agrees and promises to go see him, claiming to just need a little time, which Nathalie understands. Later, when Nathalie, Gabriel, and the bodyguard discover that Adrien isn't in his room, they immediately set out searching for him, with Nathalie making phone calls to the police and Adrien's friends. Eventually, Adrien returns home and Nathalie informs him that his father does want to spend Christmas with him and had gone to see him earlier only to find him gone. She then makes Adrien's bodyguard escort Adrien back to his room and ensure he'll stay there. Later, Nathalie is in the atelier where Gabriel tells Adrien he can't bear the thought of losing him until the doorbell rings. Answering the door and seeing many of Adrien's friends and their parents, Nathalie reveals that she informed everyone that Adrien was safe and sound. She warmly wishes Adrien a Merry Christmas and joins everyone in sharing a huge Christmas feast.
In "The Collector", Nathalie and Gabriel discover that Adrien had taken the Miraculous Spellbook from Gabriel's safe and confront him about it in his room. As punishment, Gabriel informs Adrien that he will start homeschooling with Nathalie again before the two exit the room. In his atelier, Nathalie asks Gabriel what he'll do without the Miraculous Spellbook, to which Gabriel replies by handing her a blank sketchbook and telling her to put it where it belongs. While Gabriel begins destroying his atelier, Nathalie guards the door. Adrien hears the noise from his room and rushes downstairs with his bodyguard to see what it is, but Nathalie stops them and tells Adrien that his father is very busy before sending him back upstairs to practice his piano. When Gabriel akumatizes himself into Collector, Nathalie is the first person he collects into his sketchbook. After Collector is defeated and Gabriel gets the Miraculous Spellbook back, Nathalie watches as Gabriel scrolls through a digital copy of the book and asks why he went through so much trouble if he already had a copy of the book. Gabriel informs her that he had to keep his identity safe. Nathalie then watches as Gabriel enters his lair.
In "Glaciator", Nathalie approaches Adrien as he finishes eating dinner and informs him that his father will be eating dinner in his office. As Adrien sadly goes up to his room, Nathalie reminds him to practice his piano before he goes to bed.
In "Gorizilla", once Gabriel sees that his son isn't in his room, he calls for Nathalie, who immediately appears. She and the bodyguard are scolded by Gabriel for letting Adrien leave without either noticing and ordered to find him. Nathalie quickly takes off.
In "Captain Hardrock", Nathalie listens as Adrien plays piano for his father until he makes a mistake, causing Gabriel to decide that Adrien should practice more instead of attend his friends' concert. She then exits the room with Gabriel. Later, Nathalie and Gabriel come back to listen to Adrien play, though when Adrien requests that his father play with him and he accepts, Nathalie can't help but smile.
In "Style Queen (Queen's Battle - Part 1)", at Gabriel Agreste's fashion show, she catches Marinette as she attempts to sneak out and leads her to the dressing rooms. On the way, Marinette bumps into Audrey Bourgeois, who notices Marinette's hat and asks what it is, though Nathalie informs her that they must keep going before Marinette can deny that the hat is hers. Once they arrive inside Adrien's dressing room and Marinette gives Adrien the hat, Nathalie leads Marinette to the front row seats. She spots Audrey and tells her that she has a second row seat, which infuriates Audrey as she only accepts front row seats. She attempts to fire Nathalie, but Nathalie reminds her that she works for Gabriel, not her. Audrey attempts to call Gabriel but he doesn't answer, prompting Nathalie to comment that she assumes she isn't fired, causing Audrey to furiously storm out and be vulnerable for akumatization into Style Queen by Hawk Moth. After Style Queen’s defeat, Nathalie contacts Gabriel and comments on the big risk he took involving his son getting turned into a glitter statue.
In "Queen Wasp (Queen's Battle - Part 2)", when Gabriel decides to quit being Hawk Moth and sadly sulks over his wife, Nathalie notices and hugs him. Later on, when Gabriel changes his mind about quitting being Hawk Moth, Nathalie confronts him about it. Gabriel tells her that he can’t give up, as he misses his wife too much. Though Nathalie understands, she can’t help but feel sad for him.
In "Sandboy", Nathalie is shown wishing Gabriel a goodnight before leaving his atelier.
In "Catalyst (Heroes' Day - Part 1)", after informing Adrien that she reserved the Chinese and fencing classes for him like he requested and reminding him that he must make an appearance at the Agreste Foundation Heroes Day Gala, Nathalie approaches Gabriel as he is staring at a stone statue of Emilie. After Gabriel tells her that he won't forgive himself if his plan fails, Nathalie reminds Gabriel of his promise to his wife and that he's risked so much for the chance to bring her back. She also informs him that Lila has been harboring her rage against Ladybug for months and it will be peaked now that everyone is celebrating her on Heroes Day. When Gabriel asks Nathalie if she's sure she wants to go through with it, Nathalie insists that she will always be there for him and they will succeed.
While waiting for the first part of their plan to unfold, Nathalie receives a message from Adrien requesting to go to a picnic and informs Gabriel, who agrees. Once Lila's rage hits a breaking point after witnessing an interview in which Gabriel calls Volpina a mediocre imitation, Nathalie watches as Gabriel transforms into Hawk Moth and akumatizes Lila into Volpina. Once Volpina succeeds in creating negative emotions throughout Paris, Hawk Moth deakumatizes her and creates another akuma for Nathalie. When asked if she's ready, Nathalie declares that she will go to any length to end the reign of Ladybug and Cat Noir. Satisfied, Hawk Moth akumatizes Nathalie into Catalyst, a villain who can boost his own power. Catalyst then infects Hawk Moth's cane, turning him into Scarlet Moth and allowing him to create as many akumas as he desires. After Scarlet Moth gains an army of akumatied villains and heads on top of the Eiffel Tower, Catalyst wishes Scarlet Moth good luck.
In "Mayura (Heroes' Day - Part 2)", Catalyst tells Scarlet Moth that the time has come. While observing the battle between his villains and the French Miraculous superhero team, Scarlet Moth tells Catalyst that everything is going to plan, to which Catalyst claims to enjoy watching the heroes think victory is possible. Later, as part of the final phase of their plan, Volpina creates an illusion of Scarlet Moth to distract the heroes while the real Scarlet Moth prepares to sneak up behind Ladybug and Cat Noir and akumatize them. Before attempting to do so, Catalyst tells him that he is about to triumph, though when the plan fails and Ladybug and Cat Noir revert Scarlet Moth to Hawk Moth (therefore deakumatizing all his villains), Catalyst becomes angry and rushes towards Gabriel's safe to retrieve the Peacock Miraculous. She uses it to become Mayura and sends an amok towards Hawk Moth, which infects his cane. She offers him her help, and although Hawk Moth begs her not to at first, he reluctantly agrees and a giant moth creature is formed. The moth creature uses its giant wings to push the superheroes away, therefore allowing Hawk Moth to escape and detransform. Later, a drained Nathalie is confronted by Gabriel, who reminds her that she was told never to use the Peacock Miraculous as it is damaged. However, Nathalie says that she wanted to help him all the way to the end, earning her Gabriel's gratitude.
In "Animaestro", Nathalie told Adrien at the movie premiere that he must greet the Tsurugis. She holds the tablet in which Gabriel is video chatting as the Agrestes and Tsurugis greet one another. She then leads Tomoe to an empty table where the two sign agreement papers.
In "Weredad", Nathalie approached Adrien as he was eating and informs him that he has 24 minutes to finish his meal before he has to review his Chinese lessons. When asked by Adrien if his father is too busy to eat with him, Nathalie tells him when his next scheduled meal with his father was. Therefore, a saddened Adrien heads up to his room while Nathalie can't help but feel sorry for him.
In "Oni-Chan", Nathalie notices that Adrien has come home with Lila and begins to remind him that his father doesn't like visitors. However, Lila interrupts her and asks if it would be okay to ask Adrien's father directly, though Nathalie tells her that he is very busy and must not be disturbed. However, Nathalie agrees to let her inside when Lila dupes her into thinking that Adrien needs help with his math, giving her and Adrien half an hour. Once the half an hour is over, Nathalie informs Adrien and Lila that Lila has to go. However, when Gabriel discovers that Lila was in his home, he is furious and scolds Nathalie for letting her inside. Nathalie claims that she'd thought it would be good if Lila helped Adrien review his math, but Gabriel angrily tells her that only he decides what's good for his son and reminds her that she'd been fooled by Adrien's friends before. Surprised, Nathalie asks Gabriel if he wishes to take Adrien out of school, though Gabriel says no and claims to just want to make sure Adrien isn't influenced by his friends.
In "Miraculer", Mayura waits besides Chloé's house as the rest of the French Miraculous superhero team battles Destroyer in case Ladybug hands her the Bee Miraculous. When this doesn't happen, Nathalie asks Gabriel in his atelier if he's sure about making Chloé an ally as Ladybug has become reluctant in giving her the Bee Miraculous, noting how very careful she's being. Gabriel decides that in that case, he will make Chloé force Ladybug into giving her the Miraculous by making her lose all faith in the hero so that she can be akumatized, and Nathalie suggests that they use Lila to help him with the task and Gabriel agrees.
After manipulating Lila into trying to sabotage Chloé, Mayura sent an amok to a crying baby August, creating a giant lollipop sentimonster. While the plan to akumatize Chloé ultimately fails, Hawk Moth is able to akumatize Chloé's best friend Sabrina into Miraculer, a power-stealing supervillain. Due to the villain stealing both Ladybug's and Cat Noir's powers, Ladybug decides that she needs everyone -- including Chloé. However, before Cat Noir can hand Chloé the Bee Miraculous, Mayura snatches it and tells Chloé that if she joins them, all her dreams will come true. During the battle between Miraculer and the French Miraculous superhero team, Hawk Moth tells Mayura to come back to him as she has the Bee Miraculous. However, when Mayura begins to take off, Cat Noir knocks the Bee Miraculous out of her hands and Ladybug snatches it. As she ran away, Ladybug gave the Bee Miraculous to Chloé and tells her to follow Mayura, to which Chloé agrees and transforms into Queen Bee. She engages Mayura in combat, though she manages to pin her down trying to convince her to join her team by promising that she can be Queen Bee whenever she likes. However, Queen Bee refuses and escapes Mayura's grasp. She nearly succeeds in taking the Peacock Miraculous off her, but escaped and apologized to Hawk Moth for failing, but he told her that it's okay confident that Queen Bee will change her mind.
In "Party Crasher", Nathalie drove a hologram of Gabriel to the airport for Tokyo’s fashion week. While she was contacted by the real Gabriel asking if everything was going to plan, to which she says that he will be spending the entire week in Tokyo and no one will suspect that he’s actually at home.
In "The Puppeteer 2", Nathalie enters Adrien’s room while he’s practicing piano and informs him that it was time to go to Musée Grévin. When Adrien asks if he could invite a friend, she allows him to do so. However, when he winds up inviting four friends, Nathalie allows it.
In "Timetagger", after Gabriel expressed sadness over the fact of him not being Hawk Moth in the future meaning he most likely failed, Nathalie points out that it could also mean he succeeded as the future isn't set in stone.
In "Stormy Weather 2", while helping Gabriel write a letter to Tomoe Tsurugi, Nathalie reveals that she regrets taking her job, as it has become too much for her. She also admits to feeling affection for Adrien while watching him grow over the years, sadness for Emilie as she falls deeper into an endless sleep, and admiration for Gabriel. She claims that she would do anything for the latter, no matter the cost. She suddenly begins coughing violently and falls to the floor, though when Gabriel asks her if she's alright, Nathalie gets back up and says she's fine.
In "Startrain", she alerts Gabriel to a story about the Startrain being in space on the news. Then, alerts him that Adrien and his classmates were on the train but expressed hope that Ladybug and Cat Noir would rescue him. After the heroes set the train back to earth she left with Adrien's bodyguard to pick up Adrien.