Sen Kaibara is a recommended student at U.A. High School, beginning in Class 1-B and ultimately becoming a Pro Hero. Born and raised in Tokyo, he is bilingual with fluent English comprehension. He possesses an average height, a modest athletic build, dark brown shaggy hair, and black eyes featuring thin, white irises that give him a lazy appearance, complemented by a slight tan. His distinctive hero costume includes a white windbreaker with spiral-patterned tubes, a dark blue undershirt bearing drill-patterned rings, white sweatpants displaying horizontal drill motifs, and finger-covering gloves adorned with spiral designs. Typically levelheaded and calm, Kaibara demonstrates maturity, such as advising Neito Monoma against provoking Katsuki Bakugo during the U.A. Sports Festival's Cavalry Battle. Despite his stoic demeanor, he exhibits combat enthusiasm, notably against Mashirao Ojiro. Described as an "ikemen," he occasionally displays belligerence, getting drawn into friends' antics. He respects those more skilled and voices disagreement when necessary. His Quirk, "Gyrate," allows him to rotate any body part at high speeds like a drill. This rotational force enhances his close-quarters strikes, damaging opponents and penetrating defenses. He augments this ability with specialized drill gloves, making defense difficult. During the Joint Training Battle, his gyration-based combat pressured martial artist Ojiro into defense. U.A.'s Ultra Analysis Book rates his capabilities: Power (B), Speed (B), Technique (B), Wits (B), and Brutal Thinking (A), reflecting balanced proficiency and tactical aggression. Key moments include participating in the U.A. Sports Festival's Cavalry Battle and advising Monoma, appearing in the Forest Training Camp Arc, and significantly showcasing his combat skills against Ojiro in the Joint Training Battle. He shares friendships with classmates like Kosei Tsuburaba, with whom he shares a similar disposition, and Jurota Shishida, noted for their strong connection. His Joint Training Battle teammates included Tetsutetsu Tetsutetsu and Juzo Honenuki.