When the wife of her husband's colleague falls ill, Yuria ends up taking care of her children. Although she doesn't have any children, she is confused but enjoys her new life... Her brothers, who are strangely sexually knowledgeable even though they are just children, turn their attention to the busty Yuria and turn her into a semen tank. She is repeatedly made to cum by the breeding training sex every day, which awakens her female instinct and makes her a slave to the precocious boy. What will become of Yuria?