Prior to the start of the series, Pietro became a scientist and a doctor in Atlas who had once worked with Arthur Watts and other Atlesian scientists in a project issued by Ironwood to advance the Kingdom's defenses. Looking inward, Pietro discovered a way to transfer his Aura into a robot under the "Penny Project", thus winning the challenge and having made himself a daughter: Penny Polendina.
Watching the Vytal Tournament
He is first seen briefly watching the Vytal Festival match between Penny Polendina and Pyrrha Nikos in "PvP". When Penny is destroyed by Pyrrha, he reacts with restrained emotion, gripping his chair tightly. Following the Fall of Beacon, he built Yang Xiao Long's new prosthetic arm before it was sent to her.
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Pietro is described by Maria as "one of Atlas' finest minds" that works with the Kingdom of Atlas on its technological projects, having been the one to build her prosthetic eyes and adjusting them every decade.
Upon arriving in Mantle, Maria Calavera took Ruby's Group to Pietro's Pharmacy and introduced everyone. There, he explained his business in the city; aiding the citizens by providing them prosthesis. Pietro informed them he had heard of the team through his daughter, Penny. After the Creatures of Grimm attacked the city, Pietro and Maria watched as Ace Operatives captured the Huntsmen.
After Ironwood and Ruby's group came to a mutual understanding over each other's actions, Pietro was tasked with upgrading Team RWBY's and Team JNPR's weapons and armor, fitting each new addition to the individual's needs. He also repaired Yang Xiao Long's broken prosthetic, providing a new model.
After Tyrian Callows frames of Penny during a massacre at Robyn Hill's election party, Pietro's daughter returns to his laboratory for comfort. Ruby Rose talks with Pietro about Penny's recovery from the trauma of the party. Pietro states that the footage of Penny was taken from previous incidents of her around Mantle. Pietro says that whoever was responsible for the fall of Beacon would be able to break into Mantle, but that Atlas has been upgraded. Weiss Schnee asks who might be able to break into Atlas, to which Pietro replies that it would include systems Weiss points out would be controlled by the Schnee Dust Company. Pietro expresses his concern about Penny; Ruby states that if she's dismantled, she can be reactivated. Pietro however reveals that Penny's Aura is in fact part of his. He even states if the people of Mantle get their wish to have Penny destroyed, he won't be able to bring her back with his current remaining Aura. Ruby reassures and promises Pietro that they will find the culprit.
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Fallout with Atlas
After Watts turns off the heating grids in Mantle, Pietro is present in helping citizens find refuge, offering his laboratory as a safe space from the incoming Grimm onslaught. Pietro returns to Atlas, where he and Maria help Ruby's Group escape the city after their relationship with Ironwood turns sour, joining the group himself.
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Ruby, Weiss and Maria arrive at the slums beneath Atlas to take Oscar to their new base, which is a defunct restaurant taken by the Happy Huntresses. They discuss their next course of action in which Ruby and Yang have an argument about whether or not it is worth trying to worry about the Amity Communications Tower when people are dying in Mantle and James Ironwood will never cooperate with them. Jaune calms them down and suggests they go for both Amity and Mantle, and they split up. Ruby is concerned and wants them to stick together as splitting up is what Salem wants. However, Oscar reassures her that Salem wants them to turn against each other, so as long as they are united, they are together still. Ruby goes for Amity joined by Nora, Weiss, Blake and Penny, while Jaune, Oscar and Ren join Yang for Mantle. Pietro tells them that Amity can only be activated through a terminal from Ironwood's office or a terminal in a highly classified area of the Atlas Command Center.
Pietro, Maria, and later Penny arrive at the Amity Colosseum, and the three successfully intercept the tower's launch request and begin the countdown. However, Cinder Fall, Emerald Sustrai and Neopolitan arrive via airship and enter the tower through a massive hole that Cinder burns into it next to one of the stabilizers.
After the launch, Penny engages Cinder in a fight, and Maria and Neo fight. During this, Neo reveals to Maria that she is after Ruby. Just as the tower reaches its broadcast range, it activates its stabilizers, but the one next to the hole Cinder created fails due to the damage it took.
Penny attempts to lead Cinder away from Amity Tower to keep the structure safe, but Cinder lures her back by melting some of the metal beams that hold the raised platform Pietro is on. In her efforts to keep the platform from coming loose, Penny traps herself, and Cinder attempts to steal her Winter Maiden powers. Penny manages to get Cinder off of her, breaks Neo's Aura while protecting Maria, and then faces Cinder again. Cinder and Emerald attempt to defeat Penny by using Emerald's Semblance to make her hallucinate several Cinders attacking from all sides. However, Penny's heat signature vision reveals which Cinder is the real one, and she fires a powerful laser that causes Cinder to lose consciousness.
With this, the criminals flee, allowing the heroes to notice that due to one of the stabilizers being damaged, the tower is no longer in broadcast range and will likely drift along until it touches down somewhere in the north. Penny insists on pushing the tower up just long enough for them to broadcast their recorded message, and Maria backs her up, prompting an emotional outburst from Pietro, who is terrified of the thought of Penny dying again. After a heartfelt exchange, Pietro agrees to let Penny lift the tower, realizing that his fears are holding Penny back from living her life.
Penny successfully pushes the tower up just long enough for it to broadcast a video of Ruby to the entirety of Remnant. Friends, family and strangers in all four kingdoms and Menagerie watch the video on televisions and Scrolls as Ruby tells them that Atlas is in danger and tells them about Salem. She mentions the Maidens and the Relics, assuring everyone that Theodore and Glynda Goodwitch can verify what she is talking about. She then tells everyone that Ironwood cannot be trusted.
While the message continues to play, Ironwood watches as Watts switches out a chip in Penny's sword, replacing it with one with Watts' emblem on it. As soon as he places the chip, Penny's eyes begin flickering red, and she struggles to continue pushing the tower. The tower then leaves the broadcast range, causing the video to be cut off, and Penny continues to struggle against Watts' chip. She soon loses consciousness and drops from the sky, managing to tell Pietro "I love you" just before all communications with her are lost. Pietro cries over the loss of his daughter as Maria comforts him.