Omusubiman is a wandering ronin with a triangular rice ball-shaped head, featuring dot eyes, rosy cheeks, and a pink nose. He wears traditional Japanese brown clothing, zori sandals, a greyish-blue cape, and a round straw hat. Driven by a strong sense of justice, he travels various lands assisting those in need while strictly adhering to bushido principles: justice, bravery, compassion, courtesy, honesty, honor, loyalty, and self-control. He confronts adversaries using umeboshi (pickled plums), implied to be his filling.

He is often accompanied by his young disciple, Komusubiman, whom he mentors in the samurai ways. A past storyline depicted a long-distance relationship involving gift exchanges and correspondence with Butterko. Omusubiman's popularity spawned loosely connected spin-off books and animated shorts.

In the theatrical production *Fly! Anpanman; Anpanman and Omusubiman*, he is revealed as the alter ego of Lunlun Nanda, a star child and space princess. This connects him to the character Lunlun from *Anpanman and Currypanman* and Princess Lunlun Nanda from the 1989 film *The Tear of the Sparkling Star*, where he plays a role. His theme song is *Lunlun Omusubi Benevolence*, originating from this musical.

As part of the Guinness World Record-holding Anpanman character roster for the most characters in an animated franchise, Omusubiman contributes to this extensive ensemble.