Na*Na*Ki!!

Na*Na*Ki!! summary:

The youngest of seven sisters, Nanaki's goal is to "grow another 20cm and become an adult." Now she's a senior in high school and still baffles her friends with her childish ways. But simple sincerity is Nanaki's greatest power, and friendship is the most important thing in the world to her. Problems like volunteering to be class president won't stand in her way...