Nanaka 6/17

Nanaka 6/17 (ななか6/17, Nanaka Jūnana-bun no Roku) is a 12-tankōbon Japanese manga series created by Ken Yagami and published by Akita Shoten between 2000 and 2003. An anime adaptation aired on TV Tokyo in 2003 for 12 episodes, and licensed in 2004 by ADV Films.

Plot
Nanaka Kirisato is a cold and distant 17-year-old girl, who only cares about studying and getting accepted into a good college. Her childhood friend, Nenji Nagihara, is a delinquent who often gets into fights. After a quarrel with Nanaka berating Nenji and Nenji snapped to say he never wants to see her again, Nanaka is devastated but then falls down a flight of stairs. She loses her memories and regresses to the time when she was six years old. She also thinks that Nenji made a wish to become an adult just like her. Nenji ends up having to watch over her as she goes through high school, which causes trouble and comedic situations.