Nana Osaki is a punk singer who wants to debut with her band, Black Stones (BLAST for short), where she is the lead vocalist and her boyfriend, Ren, is the bassist. Nana and Ren have lived together as lovers since she was 16. When Ren is offered a chance to debut in Tokyo as a replacement member of the popular band, Trapnest (Toranesu in Japanese), Nana chooses to continue on with BLAST and to cultivate her own career instead of following Ren, as she has too much ambition to simply be a rockstar's girlfriend. She eventually leaves for Tokyo at the age of twenty to start her musical career.
Nana Komatsu, the other Nana, has a habit of falling in love at first sight all the time, and depending on other people to help her. When her friends, and then her boyfriend, leave for Tokyo, she decides to join them a year later after having saved enough money at the age of twenty.
The two Nanas meet on a train by chance, both on their way to Tokyo. After a string of coincidences, they come to live together in an apartment numbered 707 (nana means "seven" in Japanese). Despite having contrasting personalities and ideals, the Nanas respect each other and become close friends.
Nana Osaki gives Nana Komatsu the nickname Hachi (after Hachikō, because she is weak-willed and has characteristics that resemble a puppy, and also as a joke since hachi means "eight" and nana means "seven" in Japanese).
While BLAST begins to gain popularity at live gigs, the two Nanas face many other issues together, especially in the areas of friendship and romance. The story of Nana revolves heavily around the romance and relationships of the two characters as one seeks fame and recognition while the other seeks love and happiness.