Kenji Yamaguchi, nicknamed Yamaken, attends Kaimei Private School with a tall, slender frame, short blonde bob-cut hair, and dark brown eyes. His conventionally attractive features pair with a casual style accentuated by earrings, often seen in his school uniform of green or blue pants, a turtleneck jacket, and occasionally a layered white coat.
Academically driven and sharp-witted, he fixates on outshining Shizuku Mizutani as his primary rival. Pride fuels his refusal to seek assistance, clashing comically with his notoriously poor navigation skills—a flaw he vehemently denies. Despite prioritizing social alliances through group dates and sardonic observations, his intellect remains his defining trait.
Elementary-school jealousy toward Haru Yoshida’s superior mind once drove Kenji to bully him, until traumatic encounters with Haru’s brother Yūzan forged a lasting aversion to the older Yoshida. High school finds him exploiting Haru’s generosity via delinquent associates until Shizuku’s intervention sparks respect and unrequited romantic interest.
His dynamic with Shizuku shifts from calculated charm to sincere affection, leading to repeated romantic rejections that prompt temporary withdrawal before settling into platonic camaraderie. Rivalry with Haru endures through competitive jabs and envy, softening into reluctant mutual respect by the narrative’s end.
Peer relationships remain layered: he tolerates Mabo, Joji, and Tomio as diverting yet intellectually unimpressive companions, while sister Iyo’s antics provoke prickly exchanges masking genuine fraternal loyalty. He adopts a protective role toward Shizuku, advising her during conflicts with Haru and attempting to buffer Yūzan’s impact.
Post-graduation, he pursues medicine honoring his family’s legacy, meticulously countering his directional ineptitude in professional settings. Personal trivia highlights a distaste for carrots, blood type A, Taurus zodiac, and manga-end ambiguity regarding unresolved feelings for Shizuku. His name—"intelligence" and "two"—mirrors his scholarly dedication and secondary rival status.