The page below contains MASSIVE SPOILERS of the main Breath series, read with precaution.
Fluttershy is a major character in the Breath series. She's a deuteragonist and she is present on almost all Breath stories. She's notable for being an actual character from the My Little Pony: Friendship is Magic show.
"Can I help?" -Fluttershy in Episode 3.
In the original Breath, Fluttershy makes her first appearance in Episode 2, where she is raped by Skyblack Graymane and turned into his slave. As the story progresses, Fluttershy starts showing signs of insanity.
Before Fluttershy is raped by Skyblack, she was pretty much what was seem in the show. Shy and fearful. But, after being turned into his slave, she slowly becomes a killer like him.
"Y-Yay..." -Fluttershy in episode 5.
In the reboot, Fluttershy secretly stalks Skyblack until episode 7, where she reveals that she does so and that she also loves him for his personality and being "cute".
Before that happens, Fluttershy meets Skyblack face-to-face four times, the first time in Rarity's home, the second time in Twilight's house, the third time when Skyblack goes to her house to take care of her animals, and the fourth time after Skyblack leaves the spa.
Eventually, Fluttershy becomes Skyblack's girlfriend, but only for the night, as he and her are arrested later, where they meet for the last time in jail.
Who watched the show already has an idea of how she looks like, she has a long pink mane, green eyes, yellow coat and three butterflies for cutie mark.
Those familiar to the show already know how Fluttershy is. Fluttershy, as her name says, is shy, calm and "innocent".