Ebisumaru stands as Goemon's longest-standing partner, best friend, and fellow secondary protagonist. He operates as a self-proclaimed "Ninja of Justice," adhering strictly to his own unique pace and methods. Originally wandering Japan as "Nezumi-Kozo" (Rat Kid), he joined Goemon's cause after discovering their mutual dedication to righteous acts, eventually settling in Edo at Goemon's residence.

This surprisingly pudgy ninja presents a perpetually cheerful demeanor, marked by eyes typically closed in a smiling expression and a bandana tied under his nose, creating a mustache illusion. He wears a standard blue ninja gi. His personality radiates eccentricity, whimsy, and a carefree spirit, often leading him to sleep, jump, or dance regardless of circumstances, even mid-battle. His primary passions are eating and sleeping, with a prodigious appetite evidenced by consuming 200 plates of dango in one sitting; dango skewers and onigiri are particular favorites. He speaks with a distinctive Kansai dialect, calling Goemon "Goemon-han."

Loosely inspired by the legendary Edo-period thief Nezumi Kozō, Konami redesigned the concept into the comical, overweight Ebisumaru for Ganbare Goemon 2, caricaturing employee Etsunobu Ebisu. An early non-canonical twist revealed him as a woman under a curse, but this was abandoned. He frequently displays effeminate mannerisms and wears female classical dancer attire without explanation. Ebisumaru maintains a strong belief in his own attractiveness, claims descent from American actor James Dean, and asserts significant popularity with women, traits occasionally acknowledged within the series.

In combat, Ebisumaru favors absurd, unconventional weapons over traditional ninja tools: paper fans, mallets, extendable boxing gloves, festive sign paddles, frying pans, giant spatulas, hula-hoops, gymnastic ribbons, plungers, yo-yos, and bombs. Magical abilities, termed "judo" or "ninjutsu," significantly augment his formidable prowess and high stamina. Key techniques include:
* **Chibi-Ebi:** Shrinks to navigate tiny passages.
* **Rifuru/Rifurira:** Heals allies' wounds.
* **Kobun Cow:** Summons a powerful cow relative.
* **Japanese Dance/Flapping:** Eliminates on-screen enemies or enables flight using fans.
* **Firepower/Do-Flame and Thunder power/Gororin/Pikarin:** Unleashes elemental attacks.
* **Poison Mist:** Releases toxic gas.
* **Annihilation:** Instantly kills a targeted enemy.
* **Camera Use:** Reveals intangible enemies' weak points.
His style often positions him as a "Mighty Glacier," dealing high damage but moving slower than companions.

Within the OVA "Ganbare Goemon: Jigen Jou no Akumu," Ebisumaru accompanies Goemon to investigate a dimensional castle near Edo after Omitsu's kidnapping. Traversing three floors parodying Konami franchises (Gradius, Akumajō Dracula, TwinBee), Ebisumaru transforms into characters native to each world upon entry, retaining his core personality. His role involves navigating these parodic environments and confronting challenges alongside Goemon to reach the castle's top and rescue Omitsu. His portrayal remains consistent with established eccentric and supportive characteristics.

He is a father to a daughter named Mao. His claim of James Dean ancestry represents one of the series' recurring anachronistic elements.