Komatsu came to Tokyo, looking to find her dream. Unlike Osaki, Komatsu came from a large and happy household, though her childish outlook prevented her from living on her own initially. She's the middle child of three sisters.
Her chance encounter with Osaki began a friendship which changes Komatsu's life forever. She is introduced to Osaki's band, Black Stones, and their members (Nobuo Terashima and Yasushi Takagi initially). She later even helps "Blast" to find their bassist, by drawing a poster to advertise the vacancy. Much to her surprise, she also discovers that the members of Blast were friends with the members of Trapnest, a popular rock band of which she's a very big fan. After learning of Osaki's breakup with Honjo Ren, she helps the two to reconnect after realizing that they were still very much in love with each other.
In the early stages of the manga, Nana was dating Shoji Endo, until he cheated on her with Sachiko, a co-worker at the restaurant where he works. After this he chooses to stay with Sachiko as she stood up for him when Osaki threaten to beat him up. But its hinted that they still have some feelings for each other, as shown in their meeting after Komatsu entered an engagement with Takumi.
After Shoji, Komatsu found herself caught between two men: Takumi Ichinose, the leader and bassist of Trapnest, and Nobu, the guitarist of Blast (Osaki's band). Her relationship with Takumi is not a stable relationship, rather it is a sexual encounter to fill her loneliness. She is fully aware as well that someone like her could never seriously date Takumi, but is content in knowing that she is another lover until she realizes that Nobu loves her. Although everyone believes that Hachi is going out with Takumi, they only meet fairly little in the course of their 'relationship,' until she thinks she has broken it off to be with Nobu. Until her other relationships, Nobuo was the first guy she wanted to spoil with love rather than be spoiled herself, they also share the same pure and innocent personality as stated by Nana. However when Komatsu discovers she is pregnant (revealed in chapters 25 and 26), and although she loves Nobuo, she realizes that Takumi would be in a better position to care for her and her unborn child. This is also backed up by Takumi's calm attitude towards finding out and she is given strength through this kindness, unlike Nobuo who frantically reacts much like her emphasizing that he is in no position to help her. Her child would be named Sachiko but in the end turned out to be Satsuki.
She is now the wife of Takumi (initially in name only, for Takumi delayed their wedding because of Osaki's engagement to Ren) and expecting a child. Her married name throughout the series is Nana Ichinose (一ノ瀬 奈々, Ichinose Nana?). As the time passes she finds herself realizing she truly loves Takumi, and is the other reason why she choose him rather than Nobuo, she is even satisfied being the number 1 out of 100 women in Takumi's life. Thanks to Takumi's words on her cooking when they first met, she as now decided to improve her cooking even more so and take cooking classes. She makes breakfast for Takumi everyday and draws a funny face on it with ketchup, usually stating her mood to Takumi. All in all they both seem to have a normal relationship, with quarrels and making up tanks to her naive and forgiving nature and Takumi's forgetful nonchalant nature. She hopes that she will be able to live happily, although in the future sequences of NANA she lives in Japan while he lives in London, England. Junko asks her if she will be getting a divorce, and she answers that there are plenty of reasons why she should not get one. She an Satsuki will be going to London in spring break, thanks to some information on Nana she received in the mailbox of Apt. 707 and Takumi's information on the location.
Her nickname is "Hachi" - a shortened version of Hachikō because she always tries to be kind and faithful to her friends, like the dog from the Hachikō legend. (Hachi means eight in Japanese, and the kanji for seven can be pronounced as 'nana'. This also clears up confusion between the two Nanas.) A running gag in the series is for Hachi to suddenly sprout a pair of dog-like ears and a tail whenever she's very happy.
With the reporters of SEARCH (a paparazzi magazine) snapping photos of Ren and Reira together alone, Takumi decided to do some manipulating by revealing his relationship with Komatsu to SEARCH, who decided to run that news instead. As such, the couple was formally married.
However, trouble was brewing. SEARCH's photographer decided to show Hachi photos of Nana's birth mother. Hachi then travels to Osaka to uncover the truth for herself. Although she is not able to do anything about the release of the article because she wanted to protect Shin when seeing a picture of him with a look alike Reira (she did not know it was not Reira). Her relationship with Shin is that of a mother complex, and they often role play by calling each other son and mummy, even Takumi is pulled in thanks to Hachi and has become daddy. She has been recently trying to get Nana to reconcile with Ren, and is not too far from giving birth (1-2 months left).
It is also thought that Ren is Hachi's son, since she asks Satsuki if she is going to give her brother chocolates. Although he seems to favor Reira in appearance, it is ambiguous if he is her son since she stated that although she hates everything Takumi loves she cannot hate the little boy who shares Ren's name and plays guitar for her. This leaves the question in the air, as she could still resent her own child for being an object of Takumi's love, but it seems unlikely. Takumi and Naoki also have a conversation about how it must be difficult on their children to have their family separated, and that Ren should not stay on holiday anymore but go back to Japan. All of this - and the fact that Hachi wanted to name her son after a flower, like Ren - suggests he may be her son, but it is also possible he is Takumi's son from an affair who Hachi has chosen to take custody of. What further complicates the story is that Ren appears older than Satsuki, and does not resemble Takumi the way Satsuki does; as such the question of the paternity of Hachi's as-yet anonymous first child remains.