Umi Sonoda, a second-year student at Otonokizaka Academy, co-founds the school idol group μ's. Born March 15 under the Pisces sign with blood type A, she stands 159 cm tall. Her family’s traditional Japanese arts dojo shapes her disciplined upbringing: her mother teaches dance, her father martial arts, and Umi trains rigorously in kendo, kyūdō, nagauta, calligraphy, and dance to prepare for inheriting the dojo. This instills a reserved, principled demeanor that contrasts with her idol pursuits. Initially resistant to joining μ's due to discomfort with idol attire and attention, she yields to childhood friends Honoka Kōsaka and Kotori Minami’s persuasion. Early performances trigger stage fright and embarrassment, but she adapts, crafting lyrics and choreography—including the group’s debut song, "START:DASH!!"—and initially leading physical training before Eli Ayase takes over. Her logistical planning and structured practice schedules balance Honoka’s impulsiveness, cementing their partnership as μ's leadership core. Formal speech marked by polite suffixes like "desu" and "masu" reflects her disciplined nature, prioritizing effort over shortcuts. Though strict, her actions often stem from care, such as enforcing health-conscious training regimens. Pragmatism occasionally clashes with Honoka’s spontaneity, yet their synergy drives the group. Beneath her composure lie vulnerabilities: an inability to lie convincingly—exposed during card games—and a sharp, pillow-throwing reflex when abruptly awakened. Her growth arcs from insecurity to confidence. Early reluctance to embrace fan interactions or idol aesthetics evolves into assured performances. In *Love Live! The School Idol Movie*, momentary denial of her identity to evade fans highlights lingering unease with fame, yet dedication to μ's keeps her committed. She accepts leadership roles, succeeding Nozomi Tōjō as student council vice president, and reconciles tradition with idol life. Beyond idols, she reads historical texts, avoids carbonated drinks, and favors manjuu from Honoka’s family shop. Diary entries reveal introspective reflections on archery’s meditative qualities and aspirations to merge tradition with new pursuits like baking, illustrating her balance of duty, artistry, and self-discovery.