Nathaniel Kurtzberg is a teenage boy in Miss Bustier’s class.
In “Ladybug & Cat Noir (Origins - Part 1)”, Nathaniel was one of the new students in Miss Bustier’s class. After class was over, he went to the library.
In “Stoneheart (Origins - Part 2)”, Nathaniel was seen in the classroom when Miss Bustier takes attendance until Stoneheart bursts in and captured Mylène. Later in the library, he and most of his classmates listen to Hawk Moth on live TV as he demands that Ladybug and Cat Noir surrender their Miraculouses. At first he appears frightened, but when Ladybug refuses and promises to always protect the Parisians, Nathaniel happily cheers. The next day at school, he is amused when Marinette stands up to Chloé.
In “The Bubbler”, Nathaniel was one of the many kids Bubbler forced into attending a surprise birthday party for Adrien. Though he dances at the party, he was as miserable as everyone else. Therefore, but was delighted when Ladybug and Cat Noir show up to stop Bubbler, though cheering for the duo caused him and the other partygoers to be trapped inside floating bubbles. Fortunately, he was freed after Ladybug and Cat Noir defeat Bubbler.
In "Mr. Pigeon", he was seating in the back of Miss Bustier's class listening to Mr. Damocles' announcement about the derby hat designing contest.
In “Timebreaker”, Nathaniel goes with the rest of his classmates to Trocadéro in order to watch the bet between Alix and Kim. He cheers Alix on as he wants to be done with Kim’s constant dares. However, when Alix’s one-of-a-kind pocket watch was destroyed, she’s akumatized as a result, Nathaniel was horrified as Timebreaker rollerblades towards him and his classmates. In a new timeline, he fled to safety with the other students.
In "Copycat", he was sitting in the back of Miss Bustier's class.
In "Lady Wifi", Nathaniel was in Miss Bustier's class until Lady Wifi appeared causing him and everyone to flee the school.
In “The Evillustrator”, Nathaniel was doodling a comic in his sketchbook when Ms. Mendeleiev caught him and sends him to the principal’s office. On his way, he trips and drops his sketchbook on the ground, which Chloé grabs and mocks, pointing out loud how Nathaniel obviously has a crush on Marinette. Embarrassed, Nathaniel grabs the sketchbook back from her but on his way to the principal is akumatized by Hawk Moth into Evillustrator. Evillustrator attacks Chloé in the school library with a giant hairdryer, though when Ladybug and Cat Noir confront him, he holds them back and disappears. Later, he goes to Marinette’s house and asks her out as it is his birthday. Marinette agrees on the condition that he no longer attack Chloé, to which Evillustrator agrees. While setting up for his date, Hawk Moth reminds Evillustrator not to forget to obtain Ladybug and Cat Noir’s Miraculouses and threatens him by briefly controlling his hand. However, on the date, he discovers that Marinette was working with Cat Noir to stop him and heartbrokenly calls her worst than Chloé before trapping the two in a glass box and heading towards Chloé’s house. He attacks her until Ladybug and Cat Noir show up. He battles the duo but is eventually defeated and returned to normal.
In “Rogercop”, when Chloé’s expensive bracelet goes missing, Nathaniel becomes a suspect when it was revealed that he secretly sketched the bracelet, but insisted that he didn’t steal it and was offended when Marinette suggested that he could’ve.
In "Dark Cupid", he was listening to Miss Bustier's literature lesson.
In “Horrificator”, Nathaniel helps his classmates shoot a short film until Mylène is akumatized into Horrificator. As more and more students are kidnapped by the slimy monster, Nathaniel accompanies his classmates and Ladybug and Cat Noir, though he is eventually captured himself after noticing some slime where Adrien was supposedly captured. Horrificator takes him to a dark room and traps him inside one of her slimy cocoons, but he is soon freed after Ladybug and Cat Noir defeat the monster.
In “Darkblade”, Nathaniel is seen alongside Rose as she explains to Marinette why she isn’t running against Chloé for class representative. Later, when Chloé invites her classmates to City Hall to get autographs by Jagged Stone, Nathaniel goes to the event. When Marinette points out that autographs won’t solve classroom problems, Nathaniel asks her about her campaign. However, during the event, Darkblade surrounds City Hall, leaving the students trapped inside. After Marinette comes to the rescue, Nathaniel goes with his classmates on top of City Hall. He is briefly transformed into a knight, but quickly returned to normal after Darkblade’s defeat. Like the rest of his classmates, he is less than pleased after learning that Chloé stole Marinette’s diary but even more upset when she blames Sabrina. He cheers for Marinette after she presents her campaign speech and votes for her at the class election.
In "Princess Fragrance", he was having Science in Ms. Mendeleiev's class.
In “Gamer”, Nathaniel watched as Adrien and Max compete for the two top spots in a video game competition, though when Max loses his spot to Marinette, he appears to feel bad for him. At the actual competition, Nathaniel cheers for Marinette and Max as they go into the arena and was happy when they win.
In “Reflekta”, Nathaniel is at first placed in the back of the class photo, but eventually moved to the middle row. When Juleka is akumatized into Reflekta, Nathaniel was one of the people that was transformed into her replica, though he is turned back to normal after her defeat. He then accompanies his friends in the park as they take several class photos together.
In “The Puppeteer”, while strolling the Louvre museum, he is turned back into Evillustrator by Puppeteer, though he is completely controlled by her. He battles Ladybug at TVi studio but, after Puppeteer’s defeat, he was returned to normal.
In "Antibug", he like everyone else saw that something strange was going on with Chloé.
In “Despair Bear”, Nathaniel watches Tom Dupain’s cooking lesson with his classmates until it is interrupted by Chloé, who secretly calls the fire department. As Mr. Damocles doesn’t know who called, he punishes the whole school, and Nathaniel is seen cleaning the staircase as he angrily glares at Chloé. Later, he attends Chloé’s party but is briefly taken aback when she forcefully asks him if he’s having a nice time. After Despair Bear’s defeat, Tom is invited to the party to finish his cooking lesson and Nathaniel bakes macarons.
In “Frightningale”, Nathaniel appears in the final version of Clara Nightingale’s music video.
In “Zombizou”, Nathaniel reveals that as a gift to Miss Bustier, he painted her as a superhero since she’s always there for her students, even recalling a time when she helped him and another student reconcile. He is upset upon learning that Chloé didn’t get Miss Bustier anything but even more so when he discovers that she sabotaged Marinette’s gift. When Miss Bustier is akumatized into Zombizou, Nathaniel runs from the classroom with his classmates and they eventually hide in the locker room, though he isn’t seen again until the next day.
In “Style Queen (Queen's Battle - Part 1)”, Nathaniel is seen watching Gabriel Agreste’s fashion show from the front row.
In “Queen Wasp (Queen's Battle - Part 2)”, Nathaniel is seen watching Gabriel Agreste’s fashion show from the front row.
In “Reverser”, during the school’s Art Club, Nathaniel shows the art teacher his latest drawing of Might-illustrator and Ladybug fighting Queen Wasp. When the art teacher suggests turning his drawings into comic books, Nathaniel explains that he is only good at drawing stories rather than writing. The art teacher suggests that he team up with a creative worsting, but Nathaniel says that he doesn’t know anyone into that, to which Alix assures him that there’s got to be someone out there. Just then, he meets Marc and explains the Art Club, even showing him some of his drawings, which Marc is fascinated by.
When Chloé comes into the club and makes fun of Nathaniel’s drawings, embarrassed he hides them, but was relieved when she left. Later, Marinette decides to show Nathaniel Marc’s writing in order to get the two to team up and make a comic book together, but since Marinette doesn’t tell him who wrote the journal, Nathaniel mistakenly believes that it’s from Ladybug. When he goes to the park to meet the author and finds Marc instead of Ladybug, he mistakenly believes that Marc and Marinette played a joke on him. He angrily rejects Marc’s offer to make a comic book with him and rips his journal in half before leaving. He goes to the Louvre museum and confides in Alix about what happened, though when Alix points out that Marinette is not the type to make fun of others, Naa=th began to wonder if he jumped to conclusions. Just then, Ladybug and Cat Noir show up and reveal to the two that Marc was akumatized into Reverser and is looking for Nathaniel. Nathaniel agrees to go with the duo to the Eiffel Tower. He helps Ladybug and Cat Noir defeat the supervillain and then makes amends with Marc. The next day, the two make a comic book together and show it to the Art Club.
In “Malediktator”, Nathaniel along with his classmates laugh at Chloé’s Queen Bee presentation. Later, upon learning that she was leaving Paris forever, he was momentarily taken aback but ultimately pleased by the news, happily celebrating with the school until Malediktator shows up and makes it so that a bunch of students and staff destroy the building. After Malediktator’s defeat, Nathaniel attends a party honoring Queen Bee.
In “Catalyst (Heroes' Day - Part 1)”, like most of his classmates, Nathaniel believed Lila when she says on a video chat that she’s in the Kingdom of Achu and working on a pollution-reduction project. Then, after Miss Bustier asks her students what they’ll be doing for Heroes Day and Marinette claims to be working on a macaron tasting for the entire school, Nathaniel was as excited as his other classmates.
In “Mayura (Heroes' Day - Part 2)”, after Scarlet Moth’s defeat, Nathaniel attends a picnic organized for Marinette.
In “Chameleon”, when Lila returns to class and claims to have tinnitus and need a front row seat, like most of his classmates, Nathaniel believes her lies and changed seats to accommodate her. When Marinette expresses reluctance at changing her seat and supposedly upsets Lila, Nathaniel and his classmates angrily glared at Marinette, forcing her to sit in the back. After Chameleon’s defeat, Nathaniel listened to Lila as she continues to lie about her friendship with Ladybug. Back in class, Lila tells Miss Bustier that Ladybug cured her tinnitus and she no longer needs a front row seat, so Nathaniel and his classmates all decide to move back to their original seat. Lila winds up sitting next to him.
In “Gamer 2.0”, when Max asks him to test his new video game, Nathaniel was intrigued but declines since he and Marc need to finish making several comic book pages. Nathaniel was one of the many former akumatized villains Gamer 2.0 zaps into his video game dimension. Evillustrator fights Volpina and easily wins. After Gamer 2.0’s defeat, Nathaniel and the others are freed.
In "Oblivio", Nathaniel like everyone else while on the bus heard Nino and Alya apologize for the trouble they caused as Oblivio.
In "Party Crasher", he took part in Nino's plan to throw an all boys for Adrien at the Agreste Mansion and had a great time until Party Crasher crashed the party causing everyone to flee. After the villain's defeat he helped cleaned the aftermath of the party.
In "Ladybug", Nathaniel was in Miss Bustier's class finishing the Mock Exams but was surprised along with everyone else that Marinette was accused of stealing and cheating but he like everyone else knew she would never do such a thing.
In "Startrain", he was getting ready for his class field trip to visit Big Ben clock tower in London. During the train ride he sat next to Ms. Bustier drawing a picture of her until everyone took an unexpected trip to space because of Max's mother being akumatized into the titular villain. But thanks to Ladybug, Cat Noir and their new ally Pegasus everyone was brought safely back to earth.
In "Felix", Nathaniel was on video chat with his friends talking about how they could make Adrien feel better about missing his mother and agreed with Marinette's idea about sending him a video message package.In "Miracle Queen", Nathaniel was at the Seine with his friends.