The eldest of seven siblings. After his mother turned into a demon and killed five of his siblings, Sanemi killed his beloved mother with his own hands to save Genya. He then joined the Demon Slayer Corps. Because the lifespan of a Demon Slayer is short, he told Genya not to join, but Genya wouldn't listen. Sanemi was very kind as a child, but after killing his demon mother, Genya called him a "Murderer! You killed Mom! You're a murderer, Brother!" In response, he went into the mountains alone to vent his anger by killing demons, which changed his personality. He became cold and tsundere. He has feelings for Kanae.

Her parents were murdered by a demon. Shinobu Kocho is her younger sister. Kanae has a gentle and kind personality. She is usually quick-witted but can be oblivious at times. Deep down, she knows that Sanemi is a very kind person.