Ibara Shiozaki takes to the field with her classmates from Class 1-B at the start of the U.A. Sports Festival. During the first event, the Obstacle Race, Ibara crosses the finish line fourth and moves on to the next round.
For the Cavalry Battle, Ibara teams up with Juzo Honenuki, Tetsutetsu Tetsutetsu, and Yosetsu Awase. At the beginning of the event, Tetsutetsu's team attacks Izuku Midoriya's team with Juzo's Softening Quirk to trap them, but Izuku uses his jetpack to escape.
After the Cavalry Battle ends, Tetsutetsu's team fails to qualify for the final event, with Tetsutetsu confused as to how they lost all their points and Ibara remarking that it is possibly punishment for taking the dwarfy kid's headband in such an unfair way.
After Mashirao Ojiro and Nirengeki Shoda resign from the tournament event, Midnight has the empty slots replaced with Team Kendo, but Itsuka gives the opportunity to Team Tetsutetsu, with Ibara bowing in appreciation. Therefore, Ibara and Tetsutetsu become eligible for the final: the one vs. one fighting tournament.
Ibara faces Denki Kaminari in the third match of the first bracket. Present Mic introduces Ibara as an "assassin" which she takes exception to and decides to correct him. She claims that it is her humble quest to spread good across the world, and that she would never kill her opponent. He apologizes and Ibara humbly thanks him.
The bout begins and Denki asks Ibara out on a date, promising to console her after her defeat. Denki starts the battle with his Indiscriminate Shock technique, but Ibara blocks it with her Vines Quirk and ensnares Denki at the same time. With her opponent immobilized and short-circuited, Ibara is declared the winner of the match.
For her second round match, Ibara faces Tenya Iida. She starts the battle by attacking with her thorns, but Tenya uses his Recipro Burst technique to quickly run Ibara out of bounds. She is eliminated from the tournament bracket and watches the proceeding matches with her classmates. Once the festival concludes, Ibara joins her Class in honoring the winners during the closing ceremony.
On the day of the forest lodge trip, when Neito mocks Class 1-A, Ibara is seen observing. When Class 1-B arrives at the training camp, their homeroom teacher Vlad King explains that they will be extending their Quirks and that the more they use their Quirks, the stronger they will be by breaking their limits. When Class 1-B witnesses Class 1-A's training, Itsuka asks Shota if they can observe everyone, and he explains that is the reason the Wild, Wild Pussycats are around. Later it is revealed she had been knocked out by Mustard's Gas Quirk, but she was later rescued and carried to safety.
She participates in the Joint Training Battle between Class 1-A and Class 1-B. She is put on the first round team with her classmates Kosei Tsuburaba, Hiryu Rin, and Jurota Shishida against Class 1-A team formed by Eijiro, Denki, Koji and lead by Tsuyu Asui. Hitoshi Shinso from Class 1-C is added to Class 1-A's team.
Class 1-A is concerned about Ibara as they consider her Class 1-B’s main threat. Trying to find out the position of the opposing team, Koji sends pigeons to explore and they return to tell him that Ibara is spreading her vines out, probing the area. All of a sudden, Jurota and Kosei appear and attack Class 1-A. Knowing that Koji could find them with his Quirk, Class 1-B uses Ibara as bait. In the initial clash, Tsuyu manages to capture Kosei and imprison him, but Jurota tosses Eijiro into the air toward Ibara, allowing her to capture him with her Vines. Jurota retreats, carrying Koji while muffling his ability to speak, and the two Class 1-A students are put in their jail.
Despite the capture of Kosei, Class 1-B’s team is optimistic about the outcome of the round. Jurota has a new plan to defeat the opposing team, but Ibara is opposed to using such ‘sinful’ tactics. As Jurota, Ibara and Hiryu discuss their strategy, Jurota detects that the remaining members of Class 1-A coming their way, using Tsuyu mucus to fool his sense of smell. Anticipating an attack, Ibara readies herself against the incoming threat, and sends out a dense vine growth in the Class 1-A team's direction.
Ibara captures Denki, and pulls him towards her teammates with her vines. Denki tries to attack but cannot as Ibara encloses him within a vine sphere, insulating her team from his electrical discharges. Having successfully captured Denki, Hiryu seemingly shouts to Ibara to send out some more vines, to which Ibara agrees. Suddenly, she becomes brainwashed, with Hitoshi having imitated Hiryu's voice with his Artificial Vocal Cords.
Everything turns out to be a trap by Class 1-A’s team. Denki was purposefully captured by Ibara in order to expend her ability to produce vines, leaving a window of opportunity for Tsuyu and Hitoshi to get closer. Hiryu tries to shake Ibara out of Hitoshi’s Brainwashing, but Tsuyu, who’s holding her, moves her out of range. With Ibara neutralized, Tsuyu and Hitoshi face and defeat Hiryu and Jutora. Later, Class 1-A and Ibara, still brainwashed, carry Hiryu and Jurota towards their jail, and imprison the entire Class 1-B team.
After the match, Vlad King scolds his students for not choosing either Ibara or Jurota as their team leader. Jurota apologizes to Ibara for allowing Class 1-A to complete their planning and Neito commends his classmates on their effort.