Before the arrival of his second cousin, Eriko, Ryuji Kisaragi was leading a peaceful life as an ordinary high school student. However, Eriko's arrival caused a sudden change as they embarked on an exciting adventure. After obtaining a priceless artifact box from a notorious illegal dealer, they stumbled upon a red dragon girl by the name of Rose. As Rose was being relentlessly hunted down by the black market syndicate, Ryuji fearlessly utilized his extraordinary expertise in managing relics to safeguard her.