Sanae is introduced to the series as the best friend of the main character, Hanabi. She is shown to be a supportive character in the beginning, but when they're alone, she tends to be very possessive.

Spoiler

Her ill feelings towards men began when she was almost molested by a man on the train, although saved by Hanabi, leaving her scared. Sanae begins to have romantic feelings towards Hanabi as the story progresses.