Meet Nana, a shy little high school girl with a crush on a guy named Yuichi who has a passion for photography. Poor ‘lil Nana can never work up the courage to tell him how she feels, though.
One fateful day her father comes home from an overseas trip, bringing with him a souvenier as a gift for his daughter. It is a crystal called the ‘Prism of Seven Colours’. Pretty as it is, her father warns her to never let the moonlight shine through it. Pity that Nana didnt hear him and has already frollicked off to her room to admire the purdy crystal further. Anyhow, she lets the moonlight shine through it, there is a flash of light, and all of a sudden...
There are six other girls in the room who all look identical to Nana?!
Later we discover that each Nana is not identical. They all have different personalities. There’s normal Nana, the original, and the rest are all later given names to avoid confusion. They are, Nanappe (or ‘Dynamic Nana’), Nanarin (or ‘Crybaby Nana’), Nanapon (or ‘Sexy Nana’), Nanako (Or ‘Easygoing (/genki) Nana’), Nanacchi (or ‘Mean Nana’) and Nanasama (or ‘Smart Nana). The manga is basically just day to day silliness and comedy as all the Nanas try to get along, and all clamber over eachother to get to Yuichi, with the added strain of their school entrance exams!

(Source: http://www.madhousemedia.com.au)