The Onimaro Leader appears to be a humanoid Yo-kai with grey skin, covered almost completely by a dark grey cloak.
The cloak is covered in a pattern of various symbols resemblings yellow eyes, one being directly where the face would be, almost giving this Yo-kai the appearence of having a single giant eye.
Like the name would imply, the Onimaro Leader appears in Yo-kai Watch Shadowside: The Return of the Oni King as the leader of the Yo-kai Virus known as "Onimaro", who aims to use the malice in the hearts of people to revive the Oni King Rasen.
Yo-kai Watch: Wibble Wobble
The name "Onimaro Leader" is derived from "Onimaro", and the English word "leader".