Released as a mascot and special bonus feature to the Japanese Windows 7 Ultimate edition, Nanami Madobe quickly gains fame in the otaku community as the latest and most adorable of the OS-tans. Widespread popularity was then established when the celebrated seiyuu (voice actress) and singer Nana Mizuki was hired to serve as the voice of Nanami-tan. As one might guess, the name Nanami is a wordplay on the seiyuu’s name and the Japanese prounciation of seven (“nana”).
Whatever else one might say about Microsoft as a company, you got to admit that their Japanese branch sure has awesome marketing ideas. I can’t provide factual sources here, but I’m sure willing to bet that a significant portion of the Japanese’s younger techie community — those most picky about their operating system choices — are at least moderated involved in the Japanese visual culture, better known as their anime/manga otaku culture. Making Windows 100% more moé is certainly one surefire way of making sure at least one of their machines, likely the most often used one, is running it.