Sekido is not a hostile and violent demon despite he's always grumpy and looks aggressive all the time. He has long black wavy hair that goes past his shoulders and narrow, deep red eyes. He has two prominent curved horns on his forehead. He also has the kanji of "Rage" in his tounge. Though, he's docile like Nezuko. Could change into whatever age he wants and has a bamboo muzzle in his mouth just like her.