Oneknight is a Mazin, formed when animal spirits from the Magic World combine with objects from the Human World, specifically a sword and a dog. Classified as a Tool Mazin, Oneknight stands 1 meter tall and weighs 40 kilograms, marked by a distinctive scratch on the left ear. Only wizards and residents of the Magic World can perceive Mazins like Oneknight.

This character possesses multiple abilities tied to distinct forms. In its base state, Oneknight utilizes techniques including Good Knight (S-rank), Yet Knight (A-rank), and Bark Cut (B-rank). Through Fever Evolution, it achieves the Brave Oneknight form, growing to 1.5 meters and 50 kilograms, with scratch marks now present on both ears. This form gains new abilities: Holy Knight (S-rank), Silent Knight (A-rank), and Shred (B-rank). A subsequent Legend Fever Evolution unlocks the Kaiser Oneknight form, reaching 1.7 meters tall and introducing advanced techniques Knightmare Break and Knight Elysium.

The name "Oneknight" merges the Japanese onomatopoeia for a dog's bark, "Wan" (ワン), with "Knight" (ナイト), creating a play on the phrase "one night." The evolved form "Brave Oneknight" similarly references the term "Brave Knight."

Oneknight appears in Episode 39, featuring interactions with characters like Ballonya. The character is also featured in merchandise, specifically the MZ-17 Mazica Pack toyline product which introduced the Fever Evolution mechanic.