Childhood friend of Sana Hidaka.
Out of everyone she appeared to be the closet to Sana when they were children. She even played a special unfinished song during his goodbye party. To this day she still has the headband Sana gave her during a festival.
When Sana returns he does not recongize Nanaka which earns him a slap across his face. She forgives him when she sees him play the song she made for him on the piano. The cause of Nanaka's new personality was she was the victim of arson in which she lost her parents. Everyday she would write a letter to Sana in an empty and locked up mailbox which they both discovered wishing he would he come back to save her.
She starts to open up to everyone as the story goes on, she even is more honest about the way she feels about Sana and Life. She later tries to kill herself due to emotional trauma. This is a real turning point in the anime, Sana and Nanaka tell each other their secrets and grow very close.