Having a sister who loves her Onii-chan so much that she wants to marry him in real life is nice, right? (with a blank expression) Ryushi, the son of the Demon King Astaroth, has five younger sisters. The eldest daughter is named Arissa, followed by Esmeralda as the second, Eltruge as the third, Carnaza as the fourth, and the youngest being Kururu. The five sisters loved Ryushi not just as a brother but excessively as a man. ‘I’ll become Onii-chan’s bride when I grow up’… The sisters, determined to fulfill this childhood declaration even as they grew older, consistently presented challenges for Ryushi, leading him to spend his days overwhelmed by their antics. However, Ryushi had a secret. He was not the son of the Demon King; instead, he was a human foundling whom Amon, the Demon King’s right-hand man, had taken in. The real child of Amon had died shortly after birth, and to prevent his mental collapse, Amon made a certain contract with the still-infant Ryushi… “Pretend to be the Demon King’s child until you come of age, and I’ll help you until then.” – all for the sake of survival. Ryushi had accepted this contract.