Two girls, both named Nana and of the same age, coincidentally meet on a train trip to Tokyo. They soon find theirselves living with each other under the same roof because of an even bigger coincidence. Even though they share the same name and age, they differ in just about everything else. Even so, through hard experiences in love and life, a strong friendship is born between them, as both Nanas grow through their hardships and struggle to win the odds.
Source : http://www.animenewsnetwork.com/