Nana Osaki is depicted as having short black hair, and usualy black make-up.
Nana O. was born March 5, 1981 in Tokyo. She is the illegitimate daughter of Misuzu Osaki, who left Nana in the care of her grandmother when she was four years old. Nana has not seen her mother since, and has thus forgotten what she looks like. Nana's grandmother, Miyuki, was very strict, and forbade her from wearing the colors pink and red because she did not want Nana to "tempt" men and become like her mother. Nana Osaki, however, had a rebellious streak. In high school, she was friendless until she met Nobuo Terashima, who introduced her to punk music and bands.
She was falsely accused of prostitution and was expelled when she didn't deny the charges. Nana , soon regretted her decision; she believes that the accusations led to her grandmother's fatal illness. However, as a present to herself, Nana bought her first red dress.
Nana Osaki then wore the red dress to a punk concert with Nobu, where she first laid eyes on Ren Honjo. Nana was instantly captivated by him, and accepted Ren's offer when he asked her to join the band he was starting with Nobu and their friend Yasu.
As the lead singer of the band Black Stones (Blast, for short), Nana gained a rabid following of fans in her hometown. She developed a typically "cool" appearance, wearing punk fashions and getting a lotus tattoo on her arm. She also moved in with Ren, and the two shared an intense romance until Ren told her that he had been offered a big record deal and would be leaving Blast to play with the band Trapnest in Tokyo. Though Ren and Nana still loved each other, they believed that a long distance relationship would be pointless. Nana proudly refused to abandon her own musical career to follow Ren; thus, their relationship ended.
Determined to "polish the shards of her dreams" and become a successful musician, Nana moved to Tokyo and re-formed Blast with Nobu, Yasu, and a new bassist, Shin. She also befriended Nana Komatsu, a kind-hearted but scatter-brained girl who, like Nana Osaki, wished to fulfill her dreams in Tokyo. The two Nanas shared an apartment (numbered 707, "Nana" being the Japanese word for seven) and became quite close despite their different personalities and aspirations. Nana gave Nana Komatsu the nickname "Hachi," which was adopted by their mutual friends. Nana also became fiercely protective of Hachi, going so far as to physically threaten Hachi's philandering boyfriend, Shoji. However, Nana is also somewhat possessive of Hachi, and feels jealous when anyone appears to be taking "her" Hachi away.
Hachi helped reunite Nana with her first love by inviting her to attend a Trapnest concert. At first Nana turned her down, but eventually gave in and agreed to go. For the first time in two years, Nana saw Ren in person. Ren saw her too, and they rekindled their romance that night. Nana thanked Hachi by introducing her to Trapnest's bassist, Takumi, whom Hachi idolized. However, Takumi's cold "playboy" personality put doubts in Nana's mind, and she wondered if he was a suitable partner for her friend.
It soon became apparent, however, that during the period they were separated, Ren and Nana grew apart despite the fact that they still love each other. When they use to date, Ren and Nana often shared secrets and talk with one another; however, Nana now no longer confides in Ren as much. This fact worries her because whenever she has a problem, the person she turns to is Yasu, who, in turn, often rushes to her aid regardless of the time or place. Her trust in Yasu is perhaps because throughout all the years, Yasu remained an unending source of strength and a pillar of support for her, while Ren (like the mother who abandoned her) left her behind to pursue his own dreams. It was hinted that perhaps she has never forgiven Ren for it.
As the story progresses, Blast gets a record deal at Gaia Records and is quickly thrust into the public spotlight. Nana has trouble coping with the paparazzi, especially when tabloids print stories about Ren's possible affairs and probe into the location of her long-absent mother. Though Ren proposes to Nana and asks her to move in with him, their relationship is often volatile and Nana wonders if it will last. Nana also feels Hachi slipping away, since she has moved in with her now-husband, Takumi, and rarely sees her. Nana hopes to reconnect with Hachi, and their time in apartment 707 remains special in her heart.
Subsequently, both Nanas manage to catch up, first during Reira's birthday party and later, after Hachi's official engagement to Takumi, which Nana compared to as becoming "the wife of an underworld leader".
Later in the series, it is revealed that Nana's mother is actually alive, and her whereabouts are exposed by a magazine called Search, which had previously exposed Ren and Nana's relationship to the public. It turns out that Nana's mother had actually maintained a fairly normal lifestyle and even had a child of her own, Misato Uehara. The Misato that the band knew was really Mai Tsuzuki, who borrowed Misato's name to feel like Nana's real little sister. Mai was the granddaughter of a man who was a lover of Nana's grandmother, and subsequently reading her grandfather's diary became a fan of The Black Stones and Nana. The real Misato has an incredible likeness to Nana, and when she finds out that her mother abandoned her idol, she flees in shock and disappointment.
Nana and Ren were on a break since Shin was caught smoking marijuana. Ren wanted to try to quit his addiction of drugs before making up with Nana. By the end of Chapter 77 while Ren has gone to retrieve Reira for the sake of Trapnest before meeting Nana for her birthday, he mistakes a cat for Nana and crashes. In chapter 78 it is revealed that following the car crash which concluded Chapter 77, Ren has died.
In Chapter 78-2, Yasu notifies Nana of Ren's passing by saying "I simply have no words to save you", he then tells her "Ren's dead". Nana's reaction can be understood by the closing lines of the chapter, in which she states "time stopped moving for me".
In the latest Chapter 80, Nana arrives at the funeral in a car. Unable to walk or even stand Yasu carries her into the building. Still in her collapse state, Nana is unable to speak. She can’t speak, even in front of Ren’s body. All she did was stare at his perfect hands. After the procession, Ren's manager brings in a birthday present from Ren that was found in his belongings and asks Nana to accept it. Nana silently moves onto a couch and lies down. The present remains untouched.
In recent chapters, Nana had started getting panic attacks due to stressful situations, causing her to have trouble breathing. This usually had to be remedied by putting a bag over her mouth to regulate her breathing. As of Chapter 81, she has had three panic attacks so far. Hachi wasn't aware of this problem until Chapter 81, where she helped Nana's breathing by kissing her.
- On her left arm, she has got a ren's flower due to his love that's not a lottus.
- Her name is written in katakana, a contrast to Komatsu's (which is in kanji with the second one being a symbol of repetition for kanji).
- She has been on the cover of every volume of the manga series. Also, the covers depict her activities with Hachi, which includes meeting her in apartment 707, shopping and watching a movie, among others.
- Coincidentally, the favourite designer of , the singer/actress who portrayed Nana in the live-action movies, is also . Nakashima also became good friends with , the actress portraying Reira/Layla (), which is ironic, considering that in the manga series, Nana actually dreaded having Reira/Layla around, as she felt that Reira/Layla was too cute for her comfort.
- For her portrayal of Nana in the anime, Romi Park won the "Best Main Character (female)" award at the first "". Also, at the same ceremony, , who voiced Reira/Layla, received the "Best Newcomer (female)" award (though for her role as Haruhi Suzumiya), while , who voiced Shin, received the "Best Supporting Character (male)" award (though for his role as ).