Rantarō Inadera is a first-year student at Ninjutsu Academy, hailing from a common, low-ranked ninja family. His primary goal is to become an elite ninja who aids others, though he's prone to mischief with his best friends, Kirimaru Settsuno and Shinbei Fukutomi. Their antics often disrupt class and draw instructor reprimands. He sports fiery red hair, youthful freckles, and round glasses essential due to significant astigmatism, leaving him nearly blind without them.

Serving on the Health Committee, he trains as a Combat Medic in both ninjutsu and healing arts, occasionally experiencing the committee's inherited misfortune. Academically, he struggles alongside his friends, frequently failing classes due to distractions or misadventures. Despite this, he boasts exceptional speed, holding his class's 100-meter dash record at 10 seconds, marking him as a Fragile Speedster. He also possesses artistic talent, often sketching daily life scenes as a Sequential Artist.

His personality balances dedication with a penchant for troublemaking. His catchword, "Effort," reflects his Determinator spirit. This resolve surfaces during critical missions, like undertaking a perilous overnight run on a twisted ankle to warn Sonoda Village when targeted. He shares a Boke and Tsukkomi dynamic with Kirimaru and Shinbei, exchanging puns and comedic banter. Though generally good-natured, earlier depictions highlighted a Hair-Trigger Temper, especially in manga.

His development shows increased reliability during crises. When his teacher, Doi-sensei, vanishes after a duel challenged by the Tasogaredoki Ninja Sonamon Morisuke, Rantarō observes unsettling changes at the academy, including substitute instructors Konnamon Zatto and Sonamon. Amidst a creeping "white darkness" threatening the academy's peace, his concern for Doi-sensei and awareness of the abnormal situation highlight his loyalty and growing perceptiveness. He actively joins classmates in efforts to restore normalcy to Ninjutsu Academy.