Nina Martin is the main protagonist in House of Anubis. She comes to the Anubis House at the beginning of season one at the same time Joy disappears. She meets Sarah Frobisher-Smithe quickly thereafter and quickly gets involved with all the crazy events that happen at the Anubis house. She finds herself in a club named Sibuna that's trying to uncover the secrets of the old house. It is revealed that she is The Chosen One which was once thought to be Joy.
She comes back in season two to find herself caught in another mystery that could once again cost her life.
When Nina was a young girl, both of her parents died in a car accident. As a result of this, she went to live with her Gran in America. She received a scholarship to Anubis House in England (possibly because she is a good academic student, as shown many times). However, due to an international mix-up of some sort, she arrived late. In this boarding school, she first shares a room with Patricia Williamson. Patricia constantly bullied her because she thought Nina was involved in her best friend and former roommate Joy Mercer's departure or "disappearance". Nina then switched rooms and became roommate to Amber Millington, who had fought with Mara Jaffray over Mick Campbell and had been unable to continue sharing a room with her.
She comes across as a kind, smart, and forgiving person, as she forgave Patricia as soon as she apologized and was willing to follow her into the forest despite what Patricia had done to her. She has a necklace that resembles the Eye of Horus and has a picture of a girl that Fabian Rutter and Sarah Frobisher-Smythe think looks exactly like her. She is also a member of Sibuna, founded by herself, Fabian and Amber. In the Season One finale, Nina is revealed to be the Chosen One, not Joy as the Secret Society originally believed. Being the Chosen One means that Nina is descended from Amneris, a figure in Egyptian mythology. It also means she is the only one who can reassemble The Cup of Ankh at the Chosen Hour, as Nina could successfully assemble the Cup while Joy could not; this can only happen at a specific time every twenty-five years. The legend of the Cup also stated that the Chosen One would be born when the month day and hour are the same for example nina was born on july 7th at the seventh hour but sarah frobisher smythe was bor on the first of january at one in the morning . Both Nina and Joy were born on July 7, which is why Joy was initially thought to be the Chosen One. However, Joy was born at 7:00pm, which is the nineteenth hour and Nina was born at 7:00am. For some reason, Sarah knows Nina's name without Nina mentioning it to her; this might be due to the fact that Sarah identifies Nina as the Chosen One almost as soon as she met her. In the Sibuna Fire of Sacrifice, she throws in her lucky mascot after protesting Amber's idea. She is one of the seven acolytes that would have been sacrificed in order for the Society to gain immortality. She and Fabian share their first kiss at a prom that Mara and Amber organize for the end of term, also known as "End-of-Term Prom". Nina and Fabian are chosen as Prom King and Queen by Amber, who always wanted to be Queen but decided Nina deserved it. They dance and the Cup is shown under the stage.
In Season Two, she discovers she has a counterpart, like the sun and the moon. This person is called the Osirian. It was rumored the Osirian would be Fabian but Senkhara thought it would be Eddie Miller. It turns out Eddie is the Osirian, leading to him being protective of Nina. She sees many ghosts in this series and Sarah, who has died, contacts her through the dollhouse. She has a rivalry with Joy due to Joy's romantic advances for Fabian. They were prompted to discuss how their relationship was going and they broke up. Nina was heartbroken when she saw Fabian kiss Joy, but they got back together in the series two finale.
In Season 3, it was discovered during the summer that Nina and Eddie had to be kept apart. Nina didn't get in contact with anyone except Eddie. Fabian and Nina were going to have an American date but Fabian never got there because the plane ticket was too expensive. Amber, Patricia, and Joy think that Nina wasn't responding to anyone because of Fabian not getting to America, but they were wrong. Mr. Sweet comes to the House, and him and Trudy announce Nina will not be coming back and that is all the information they know. Nina soon contacts and chats with Fabian online using "Chumchatter" and Nina said that Eddie has a letter for Fabian that she wrote but Edde lost it and Fabian thinks that Eddie's hiding something. Fabian sneaks into Victor's office during class and finds Nina's file that has information about the Chosen One that he takes and steals. Him and Patricia soon discover that Eddie has Nina's locket. Patricia then sneaks onto Eddie's laptop and Nina sent Eddie a message that says they can't be together anymore so Patricia and Fabian suspect that Eddie and Nina had a summer romance and Nina's given Eddie the locket to remember her by. Soon at the end of House of Arrivals/House of Presents, it is said that the Chosen One and Osirian can't be together after Fabian almost beats up Eddie in front of the Anubis House students. Eddie and Fabian find the letter in Eddie's shoe and Eddie leaves Fabian to read it. Fabian can't bring himself to read it and he asks Amber to read it to him in House of Truth/House of Hieroglyphs. In the letter Nina explained she had decided not to come back to the house because the Chosen One had to stay away from the Osirian and because her Gran was ill again. She told him she'll always love her first love, but urged Fabian to move on. In House of Awakening/House of Sarcophagi, Fabian lures Mr. Sweet away from his office saying that he misses Nina.
- She is the only American student as of season 1.
- She is one of the three founding members of Sibuna, the others being Fabian and Amber.
- Nina's birthday is July 7th, the same day as Joy's.
- She was born twelve hours earlier than Joy.
- She and Joy have both shown interest in Fabian.
- She is one of the three girls Fabian has been rumored to have romantic interest in, the others being Joy and Patricia.
- Nina's Dutch/Belgian counterpart from Het Huis Anubis was Nienke Martens.
- She and Harry Potter share similarities, such as both believing their parents were killed due to a car crash, both attend British boarding schools and have special magical objects (Harry: Wand, Nina: Locket). Both also wander in the night.
- She could be from a royal Egyptian bloodline since Jerome mentioned the Chosen One is from a specific bloodline.
- Her locket has no power in other hands but it seems to have an eerie magic ability to open secret places around the house that aid in the search.
- She is not very close to all of the students, like Joy, Mick, and Mara.