On a romantic getaway, newly dating Tomoki and Yukino find themselves stranded after their car suffers a flat tire. Seeking assistance, they arrive at the enigmatic Black Rose Mansion, where they are warmly welcomed by the captivating Mistress Mari. Her gracious hospitality and alluring presence draw the couple into an unexpected evening of intrigue and temptation. As the night unfolds within the mansion's elegant halls, the boundaries of their relationship begin to shift in surprising ways.