Kotetsu is a servant of Mikage Shrine, a type of spirit known as an Onibi-Warashi, which translates to will-o-the-wisp child. Alongside Onikiri, he serves Nanami after she becomes the shrine deity. Kotetsu has a very joyous and happy personality and is also quite caring, frequently showing concern for the well-being of both Tomoe and Nanami. He appears as a small, bald childlike yokai wearing a mask, but like Tomoe, he is able to shapeshift into other forms. He is extremely fond of Nanami and Tomoe and remains a loyal attendant throughout the series. His role is that of a supporting shrine spirit who helps maintain the shrine and looks after the main characters. Kotetsu does not undergo significant personal development, remaining a cheerful and constant presence. In terms of abilities, he possesses the typical yokai skill of shapeshifting and likely other supernatural traits common to his kind, though these are not extensively detailed.