Kenjiro Shirabu played volleyball at Toyokuro Junior High alongside Shunki Kawatabi, with his team anticipated to excel in tournaments during his time there. Initially inspired by strategic setters like Oikawa Tooru after observing a Shiratorizawa-Kitagawa Daiichi match, Shirabu redirected his ambition upon seeing Ushijima Wakatoshi’s dominant power and height. This encounter cemented his determination to attend Shiratorizawa Academy solely to become Ushijima’s setter. Without a sports scholarship, Shirabu focused intensely on academics for admission. Already a top student, he amplified his efforts to clear Shiratorizawa’s demanding entrance exams. This scholarly discipline paralleled his athletic evolution, where he deliberately abandoned a flashy, fast-paced style for a restrained approach featuring consistent high tosses to optimize Ushijima’s spikes. As Shiratorizawa’s second-year starting setter, Shirabu exhibited layered traits. Outwardly deferential to upperclassmen—especially Ushijima—he routinely clashed with first-year wing spiker Tsutomu Goshiki, condemning the latter’s showboating. Despite a poised exterior, he displayed volatile competitiveness during matches, easily provoked by rivals like Tsukishima Kei’s stubborn blocks. His tactical intellect enabled rapid recalibration under duress, such as slapping his own face to refocus mid-game, startling teammate Tendou Satori. At 174.8 cm, Shirabu stood shorter than most teammates and voiced a wish for greater height. His court presence blended shrewd intensity with efficiency-focused play, rejecting any implication he was merely Ushijima’s accessory. This defiance surfaced when he executed a setter dump to bypass Tsukishima’s block, quietly asserting autonomy. Yet his loyalty to Ushijima stayed paramount, anchored by a vow to prioritize setting for the ace—a promise Ushijima reiterated during matches. In the Spring High Preliminary finals against Karasuno, Shirabu endured severe mental pressure. Tsukishima’s targeted blocking fractured his rhythm, culminating in a critical error: a low set to Ushijima that became a match-losing block. After a sharp reprimand from Coach Washijo, he steadied himself for later sets. Post-match exchanges revealed team complexities, like his blunt query about Ushijima’s utility during a timeout—drawing Semi Eita’s fury but highlighting Shirabu’s pragmatism. Post-graduation, Shirabu entered medical school. By November 2018, he reached his fifth year of study, sustaining his trademark academic rigor. His appearance remained consistent after the timeskip.