Sen Kaibara/Synopsis

U.A. Sports Festival Arc
Sen comes in 22nd place during the Obstacle Course, allowing him to participate in the next competition. For the Human Cavalry Battle, he teams up with Neito Monoma as the rider, Kosei Tsuburaba, and Shihai Kuroiro..

Unlike the rest of Neito's teammates, Sen is the only one to call him out for taunting Katsuki, explaining that the latter would've made the same immature move. Despite all their efforts, Team Monoma loses all of their headbands to Team Bakugo, which prevents Sen and the rest of his team from advancing to the tournament.

Forest Training Camp Arc
Sen is present along with the rest of his classmates when Vlad King instructs them on Quirk Training upon their arrival at The Beast's Forest, explaining that the more they use their Quirks, the stronger they will be by breaking their limits.

When Class 1-B observes Class 1-A intense quirk training to push beyond their limits, the Wild, Wild Pussycats appear to explain that they will be there to help and guide them in their training.Tiger decides to call any simple power augmenting Quirks to go to him, in which Sen and Jurota Shishida dread at the sight of seeing Izuku training to the extreme. Sen notes that Tiger is rather scary in terms of appearance and demeanor.

On the 3rd night of the training camp, Class 1-B acts as the scaring group during the "Test of Courage". However, the Vanguard Action Squad arrive to interrupt the fun by invading the Beast's Forest in search of Katsuki. When Mustard emits his Gas Quirk, Sen is one of the many Class 1-B students that get knocked unconscious by its effects. He is seen next to Kojiro Bondo in the aftermath of the battle, being rescued later by Shota during the aftermath of the Vanguard Action Squad Invasion..

Shie Hassaikai Arc
Neito Monoma reveals that all of class 1-B have passed the Provisional Hero License Exam.

U.A. School Festival Arc
Sen help his classmates to organice and prepare the play "Romeo, Juliet and the Prisoner of Azkaban: The Return of the Kings!" for the U.A. School Festival, although he does not participate in the actual performance.

Joint Training Arc
Sen and the rest of Class 1-B are all present for the Joint Training Battle, with Neito loudly claiming that the momentum is now moving to their side. Upon selecting teams, Sen is teamed up with Tetsutetsu Tetsutetsu, Pony Tsunotori, and Juzo Honenuki and they will face Class A's team of Tenya Ida, Shoto Todoroki, Mezo Shoji and Mashirao Ojiro at Round 3.

Upon entering the battlefield, Tetsutetsu feels his way around Ground Gamma. He says that despite being considered dull he still got into U.A. High's hero course. Sen asks what's gotten into Tetsutetsu and the latter claims their team doesn't have good information gatherers, deciding to tear his way through the field to challenge Class 1-A head-on. Sen calls out Tetsutetsu for charging directly at their opponents without thinking about the flaws of his plan. Juzo then tells his teammates that Tetsutetsu's strategy plays right into their abilities.

Sen and Pony disagree but Juzo's flexible attitude gets them to go along with Tetsutetsu's brashness. The battle starts off with Shoto Todoroki unleashing a giant ice wall at the opposing team, in which Juzo retaliates by turning it into liquid substance with his Softening Quirk. This allows Team 3-B to advance towards Team 3-A. Sen then activates his Gyrate Quirk to fight against Mashirao Ojiro.

Sen appears to be gaining upper hand as his drill attacks keep Mashirao at a heavy disadvantage. However, his attack is quickly halted by Tenya Ida, who swiftly drags him towards Team 3-A's prison cage. Sen gets upset over Ingenium interrupting his "one-on-one fistfight" with Mashirao, in which the latter reminds him that he should treat the exercise as if it was an actual battle in reality.

Tenya manages to successfully send Sen to Class 1-A's prison cage. However, Sen remains defiant until the end by continuously attempting to break free of Tenya's grasp, which heavily slowed down his opponent's movements. Vlad King later announces Sen as the MVP of Round 3, much to the latter's annoyance. When the match ends, it turns out that Sen and Mashirao are the only ones that were actually captured.

After their defeat, Sen stays to watch the last round along with the rest of the students. The Joint Training Battle ends with victory for Class 1-A. In the evening, Class 1-B visits Class 1-A's dormitories for dinner and spending time with one another. Sen is shown chatting with his friend Kosei and Denki Kaminari as the two classes appear to be getting along.

Endeavor Agency Arc
With the start of the second Hero Works-Studies, Sen teams up with Togaru Kamakiri and Kosei Tsuburaba during U.A. High School's winter break.