High school student Toujo Basara's life has taken a turn for the strange. Although hesitant about his father's sudden decision to remarry, he can't deny it comes with a couple perks—drop-dead gorgeous step-sisters…who also happen to be members of a demon clan! Mio Naruse is a Demon Lord and Maria Naruse her succubus servant. Chaos and passionate antics ensue as Basara gets acquainted with his new demonic siblings, trying to protect them from dangerous demon rivals and struggling to keep up with their lusty, devilish appetites.