|Only one eye?! It prioritized one eye to accelerate the healing… Is that even possible?|
|— Petra's last words.|
Petra was a relatively short woman. She had light-ginger hair and amber-colored eyes. She wore the typical uniform of a member of the Scout Regiment, with a white button-up shirt underneath.
Petra was kind and caring, as shown when she looked after and guided Eren when he was first admitted to the squad. She seemed to have acted as some sort of attachment figure for Eren among Levi's Squad as she was the one shown to worry about him. Although all of Levi's squad wished (and demanded, to an extent) Eren's unconditional trust, it was ultimately Petra who convinced him to do so.
Despite her kind nature, Petra was a conditioned soldier with a quick reaction time against perceived danger, such as the time when Eren accidentally transformed into a half Titan, she took an extreme reaction and interrogated him alongside her squad. She also displayed extreme loyalty to her leaders and superiors and their orders.
She also showed the most remorse over her reaction to Eren's accidental transformation. Along with her comrades, she had bitten her hand just like Eren, signifying that they had established a close bond.
During the 49th expedition beyond the Walls, Petra and Oruo overhear Hange Zoë's request to capture a Titan alive be rejected by Erwin Smith while they are tending to the regiment's gear. Oruo's attempts at insulting the Section Commander result in her choking him before leaving, and Petra begins criticizing Oruo for his immature behavior. She is interrupted by Eld Gin, who orders her to continue refilling the gas tanks for their ODM Gear.
When Hange breaks away from the regiment to pursue a Titan on her own, Erwin sends Levi's squad to keep her safe. They pursue the Titan to a clearing where it is killed, and Petra notices the headless body of a Scout Regiment soldier, seemingly enshrined in a nearby tree by the Titan they had been pursuing.
Following the expedition, Petra accompanies Oruo as he goes to apologize to Hange for insulting her during the expedition.
During a scouting mission outside of Wall Rose, Petra, Eld and Gunther Schultz act as reinforcements for Levi when he goes to rescue a soldier that has been caught by a Titan. Petra is left to tend to the soldier's wounds as her comrades fight off the Titans, but is unable to stop his bleeding. She helps Levi comfort the man as he dies, and assures Levi that the soldier heard his words before he died.
After the post-Trost District battle trial to decide Eren's fate concludes with Eren joining the Scout Regiment, the Special Operations Squad, is assigned to look after Eren. Petra, along with the rest of the squad, accompanies Eren to the former HQ of Scout Regiment, which will now serve as a hideout for Eren. As the hideout has not been maintained well, Levi orders everyone to begin cleaning. During the cleaning, Petra makes small talk with Eren, cheerfully noting the disconnect between the image of Levi that the public has, and what the man is actually like.
Later that day, while the squad discusses the upcoming expedition, Hange arrives and Eren asks her to explain her experiments with Titans. Petra and the rest quickly leave the room, already painfully familiar with Hange's long-winded speeches about Titans.
The next day, Petra, along with the rest of the soldiers, arrives to the crime scene after being notified about the killings of Sawney and Beane. She is among the Scout Regiment soldiers present when Erwin attempts to recruit cadets to the regiment. During Erwin's speech, Petra and Miche Zacharius present a diagram of the path from Calaneth District to Shiganshina that the regiment will take to the prospective recruits.
Levi finds a way to contain Eren in his Titan form without killing him, allowing Hange to run experiments on him, which Petra and the rest of the squad monitor. Eren is unable to transform for some reason, but later triggers his transformation while attempting to pick up a teaspoon. Petra and the rest of his squad mates immediately prepare to kill Eren, believing he has betrayed them, but Levi keeps them at bay. Later, Hange reveals to everyone the secret behind Eren's transformation. Realizing their mistake, Petra and others bite their hands as a form of punishment, showing that they can trust each other.
One month later, Petra is part of the expedition that heads into the Titan territory. As time progresses, the news of a mysterious Titan killing the soldiers reaches the Levi Squad just as Petra and others witness the black smoke signal, knowing that an abnormal Titan is near their position. Eventually, they enter the forest. Eren questions this, but then notices Petra and others also do not know what is going on. At that moment, the mysterious Female Titan reaches their location. As they are being chased, Petra and the other squad soldiers beg Levi for orders, proposing to take the Titan down as it slaughters the reinforcements from behind. Levi, however, just shoots a sound grenade to calm them down, reminding them of their job. Eren finds himself to be unable to comply with the orders as he watches more soldiers to be killed. His intentions are made clear when he is about to bite his hand. Levi tells him to choose whether he believes in himself or the squad. Eren decides to go with the squad, and as the Titan is about to catch up with them, they reach the location of Erwin and other soldiers who manage to trap the Female Titan, much to the surprise of Petra and the squad. They then brag to Eren, claiming that it is thanks to the power of the Scout Regiment that they managed to capture their foe.
Afterward, Eld and others discuss Erwin's decision not to tell the soldiers about the plan. Eren wonders why is it that not even the elite soldiers were told about it, angering Petra and Oruo, but Eld agrees with Eren, stating that Erwin must have had a reason. They realize that if they answered Erwin's mysterious question back then, they would probably be trusted enough to be let in the operation.
Afterward, the squad begins to retreat back to their horses, when a flare leads them off-course. They are then ambushed by an unknown person who murders Gunther Schultz before they transform back into their Titan form. Eren is ordered to flee while the surviving squad members engage the Titan in battle. Petra and the others initially have the upper hand since they blind the Female Titan with the omni-directional mobility gear's gas and cripple both her arms, making them useless. But when Petra and Eld Gin move in for the kill, the Titan suddenly regenerates a single eye (demonstrating a previously-unknown ability to focus healing into fewer body parts to speed up the regenerative process as a defensive tactic) and bites Eld in half, killing him.
Paralyzed from shock and despite Oruo's pleas, Petra is unable to react in time to the Female Titan's kick, which breaks her spine and splatters her against a tree. Her corpse is seen by Levi with a silent expression when he tracks down the Female Titan. Levi would release his fury later while fighting with the Female Titan.
During the Scout Regiment's retreat from the 57th expedition, Titans give chase after the surviving soldiers. In order to escape, Levi orders the troops to abandon the bodies of the deceased so that the weight would be lifted off from the wagons and they can go faster. One of the bodies that are disposed of is Petra's, whom Levi had been watching over.
She was a skilled and experienced warrior using the omni-directional mobility gear and had a high kill record of Titan kills (58 Titans killed, 48 in team and 10 in solo), being one of the highest known in the series so far. For that reason, she was handpicked by Levi to take part of the Special Operation Squad. Her coordination with Oruo and Eld was almost perfect, as they were close to defeating the Female Titan by themselves.
- Levi Ackermann - Petra was hand-picked to be part of the Special Operations Squad. Petra expressed great admiration for her captain, and criticized Oruo for imitating him. She noted that many people are surprised upon actually meeting him and admitted that he does not live up to the legend of 'Humanity's Strongest Soldier' due to his many personality quirks and flaws. It was revealed after her death that she wrote to her father about her wish to devote herself to Levi. Petra's closeness to Levi led her father to believe she was considering him for marriage.
- Eren Jaeger - Initially, she was uneasy around him and drew her swords on him when he accidentally transforms. However, after learning that it was a mistake, she apologizes for her behavior and bites her own hand to acknowledge him as a comrade. She quickly took him under her wing, and acted as an almost maternal figure during his month with the Special Operations Squad. During the mission in the forest, she repeatedly asked him to place his trust completely in his comrades and wished for him to believe in her. Petra's death deeply affected Eren.
- Oruo Bozad - Petra and Oruo were frequently at odds, often bickering with each other. She was highly critical of his attempts to imitate Levi, and demanded that he stop. She also stated that he should bite his tongue off and die. However, beneath this seeming-hostility was a strong bond of trust born from their many missions together. He also told Petra, "You're still ways to go to be fitting for my wife." His horror after her death, and attempts to mimic the man she admired hints that he may have harbored feelings for her.
- Eld Gin and Gunther Schultz - As comrades, she had great faith in them and cared deeply for her comrades. She was enraged after Gunther was murdered, and repeatedly challenged the Female Titan while swearing revenge. Eld's death similarly shook her and caused her to panic and freeze, which eventually led to her death.
- Petra was the only female in the original Special Operations Squad led by Levi.
- Her name is Greek in origin, written "Πέτρα" and meaning "rock" or "stone." it is also the name of an ancient city in the region that is now Jordan.
- Her 58 total Titan kills is the highest confirmed so far in the series; although only 10 have been in solo and 48 in team (a record too). In solo, the record belongs to Oruo with 39. Nevertheless, Levi as Humanity's Strongest Soldier is assumed to surpass both of them, but his total statistics have not been revealed.
- According to Eld, Petra cried and soiled herself during her first mission with the Scout Regiment.
- Hajime Isayama has stated that Petra and Oruo were from the same batch of cadets.