It’s an odd mix of an unconventional Magical Girl comedy series and a parody of the Superhero genres. Nanako is a young girl, she has superpowers, but has also lost her memory. She's found by a greedy and opportunistic Teen Genius student named Yotsuya who promises to help her get her memory if she will join his detective agency. In reality, he only wants to use her powers for his own personal gain and for his agency, although the naïve Nanako is unaware of it. Meanwhile, Yotsuya's short, nerdy best friend Iidabashi falls in love with Nanako. Throughout the story, Nanako will face several bizarre villains who are also interested in her for various reasons.
Enoki Films currently holds the rights to the series worldwide (along with most of MIC's productions), and the international title for the series is Nana the Supergirl, which was the name used for its distribution and TV airings in Italy, France, Germany and Russia.
The series provides examples of:
- All Love Is Unrequited: Iidabashi is secretly in love with Nanako who is secretly in love with Yotsuya.
- Amnesiac Hero: Nanako has lost her memory and Yotsuya has promised to help her get her memory back. She doesn't know that he's just using her for selfish reasons.
- Anime Hair: Yotsuya, a boy with very long and curly pink hair.
- Badass Adorable: Despite being very strong and overpowered, Nanako is much more emotionally vulnerable than the usual heroine.
- The Cameo: Hideo Azuma's other manga/anime heroine, Pollon, makes a cameo in episode 16.
- Dude Magnet: It seems like almost all the guys want Nanako, villains included.
- Extreme Doormat: Nanako is way too nice for her own good, so it’s easy for other people to take advantage of her.
- The Ingenue: Played straight with naïve and innocent Nanako.
- Magical Accessory: Nanako's particular belt that can turn her into a "supergirl".
- Magical Girl: Nanako, although she's more like a Super Hero, lacking a Mentor Mascot, Transformation Trinket, or most things usually associated with the trope.
- Most Writers Are Writers: Iidabashi is an aspiring manga writer.
- Pink Heroine: Nanako's supergirl costume is pink.
- Red Is Heroic: Nanako's cape and insignia are red.
- Robot Buddy: 7 and 11, two robots designed by Yotsuya to assist Nanako.
- Superhero: They give Nanako a costume and call her "Super Girl" to help them fight crime. She can fly and has many other superpowers.
- Teen Genius: Yotsuya is a genius who is still a high school student.
- Two Guys and a Girl: The three main characters, Nanako, Yotsuya, and Iidabashi, including sort of a Love Triangle between them.
- Villainous Crush: Many of the villains appear to have this for Nanako.