Ojarumaru Sakanoue (坂ノ上おじゃる丸 Sakanoue Ojarumaru) is the main character and protagonist of the anime. He is a young 5-year-old nobleman of Yōsei-kai in Heian-chō and the only child of the Sakanoue family. He has a fear of water.
Ojarumaru has light skin, black eyebrows, and brown hair. He wears a sokutai, a dark blue eboshi, and green shoes.
When sleeping, Ojarumaru wears a pair of light yellow pajamas.
Ojarumaru is spoiled, laid-back, lazy, inquisitive, whimsical, and has a bit of a selfish side. He prefers a slow, peaceful way of living; he spends long periods of time relaxing or napping on his Santen Set. He strongly dislikes effort, as evident of his constant dependence on other characters (such as Kazuma) to carry him on long walks, as well as his procrastination on doing his homework assigned by Akamurasaki Shikibu. He has a habit of collecting rare items and storing them in his eboshi.
Since he was born to an aristocratic family in the Heian era, Ojarumaru speaks archaic polite Japanese, referring to himself as Maro (麿; official written in katakana as "マロ") and other people as Sochi (ソチ). He ends most of his sentences with the polite copulas, de ojaru (でおじゃる), ka no (かの), nou (のう), ja (じゃ), ja no (じゃの), no ja (のじゃ), or tetamo (てたも). Like many kids his age, he mispronounces unfamiliar words and gets corrected by either Denbo or Kazuma.
He has a habit of saying Oja (おじゃ) as an exclamation, Ojahoho (おじゃほっほ) when delighted, Ojazozo (おじゃぞぞ) whenever he is disturbed by Princess Okame's presence; and Ojabu (おじゃぶー) when sulking.
Denbo is Ojarumaru's caretaker. They have a close relationship. Ojarumaru tends to take advantage of Denbo's role as a caretaker by bossing him around.
Ojarumaru has a brotherly relationship with Kazuma. He likes spending plenty of time with Kazuma, even when the latter is busy. Whenever they are outside together, Ojarumaru likes riding on Kazuma's back or his backpack. Sometimes, they quarrel over trivial issues, but they always reconcile and remain friends.
Foes and rivals
Ojarumaru's archrival is the Kooni Trio. The Kooni Trio constantly pester Ojarumaru into returning Enma Daiō's scepter. Each time, Ojarumaru refuses. Ojarumaru always evades the Kooni Trio's efforts of retrieving the scepter by force. Ojarumaru calls the Kooni Trio a variety of nicknames; the trio as Kooni mera (子鬼めら); Aobē as Aoi no (アオイの); Kisuke as Hiyoko (ヒヨコ), or Kiiroi no (キイロイの); and Akane as Akai no (アカイの).
In the Japanese version, Ojarumaru was originally voiced by Hiroko Konishi from the 1st series until the final episode of the 3rd series. After Konishi retired from the role after a dispute over her voice recording used for various Ojarumaru merchandise, she was replaced by Chinami Nishimura from the 4th series onwards.