In the depths of the underworld resides a fierce demon known as 'Debby the Corsifa,' thirsting for battle. Unmatched in combat, she grows weary and sets her sights on Earth, intent on eradicating humanity. However, fate leads her to a bored human, Rokurou Sugo, yearning for entertainment. Seizing the opportunity, Debby challenges Rokurou to a seemingly impossible duel. In a twist of survival instinct, Rokurou proposes a game of 'Old Maid' as a less lethal pastime. Despite her warrior aura, Debby unveils a surprising ineptness for anything beyond battle. Determined to conquer Rokurou in this unexpected showdown, she persists in the playful rivalry, refusing to surrender until victory is hers.