When they were middle schoolers, Mizuto and Yume were a completely normal couple. Between flirtations and shouting matches for minor reasons, the two students stayed together until they entered high school, where they finally decided to break up. What they do not know is that fate sometimes has many surprises in store, and that they will be reunited again as stepbrother and sister only after two weeks.
Indeed, their respective parents are about to remarry and the former couple will have to live under the same roof on a daily basis. In order not to hinder their parents' happiness, they accept the situation and decide to put in place the rule of brothers and sisters, according to which the first who feels attraction towards the other loses.
