七子（苍井优 饰）和七生（知念侑李 饰）是同父异母的姐弟，因为家中一连串的变故，这对彼此之间毫无情亲可言的姐弟住进了同一屋檐下，两人共同由七子的母亲照顾。对于这个未曾谋面的弟弟，七子的内心里充满了厌恶，自觉母爱被分走的她对七生十分冷淡。 　　不幸接踵而至，七子的母亲因为绝症住进了医院，空空荡荡的家里只剩下关系紧张的七子和七生两人。随着时间的推移，七生的懂事与善良逐渐感动了七子，母亲的死讯传来，悲痛中，早已情同手足的姐弟两决定在之后漫长的时光里相依为命。可是，就在这个节骨眼上，七生在狱中的生母提前出狱了，她要将七生接回家，离别再度降临。

Nanako is an ordinary high school girl who lives with her mother, who is a taxi driver. One day, suddenly she has a younger brother - Nanao, the son of her late father's mistress. While Nanao's mother is being put in jail, Nanako's mother decides to take care of him. Nanako doesn't like it at all. Everything Nanao does irritates her. Shortly afterwards, Nanako's mother becomes very sick. In fact, she doesn't have much time left. Since she is in hospital, Nanako is forced to live with Nanao alone...