Saotome Junko

Japanese name:	早乙女淳子
Nickname:	Jun

Nana's sensible, no-nonsense best friend. Junko is much more emotionally mature than Nana and often pushes her to be more independent and responsible. She's the host of the omake (bonus) section at the end of each manga volume, reading fan mail and displaying fan art. She's often called "Jun" by Nana K.

Wikipedia