Important Hair Accessory

A character (almost Always Female) gets (or removes) a hair accessory to symbolize her Character Development.

One of the most common variants involves a shy girl sweeping her bangs back under a headband, allowing us to see her full face and symbolizing her newfound self-confidence. Because Every Girl is Cuter With Self Confidence!

Can also apply to hats, goggles and certain other forms of headgear. If it's removing a hairpiece that's significant, it may be accompanied by a Hair Flip.

Sub Trope of Expository Hairstyle Change. Sister Trope to Important Haircut.

Anime and Manga

 * Orihime Inoue from Bleach and her hairpins, which double as Tragic Keepsakes. When she grows some more she uses them as lapel decorations instead.
 * Once Naruto becomes a member of Team7, he stops wearing his goggles.
 * And Sakura starts properly using her headband when she decides to give her fullest in her fight with Ino. Who does likewise.
 * In One Piece, all of the Straw Hat Pirates except Luffy have different outfits when they reunite after two years of separation. Among the changes related to the tops of their heads: Usopp loses his sniping goggles and replaces his hat with a clean white one; Franky shaves his pompadour into a buzz cut, though he can regenerate the pompadour at any time; Chopper now wears a thick baseball cap instead of a top hat; and Sanji's hair, which once covered his left eye, now covers his right eye instead.
 * In Spirited Away, Zeniba has Chihiro's companions make a new hair tie for her, replacing her previous one. It's still in her hair when she returns with her parents to the normal world, proving that the experience was not All Just a Dream.
 * Nanoha Takamachi and Fate Testarossa exchange hair ribbons in Nanoha Original once they become friends.
 * Haruhi Suzumiya sticks with the yellow hair ribbon once she begins the SOS Brigade.
 * In the Grand Finale,  from Madoka Magica is seen using
 * In Saint Beast, Judas makes a hair tie for Shin to keep his hair out of the way when he plays harp. It's important because it shows their growing bond and he never goes without it after that.
 * The bells that Asuna wears in her hair in Mahou Sensei Negima were given to her by Takamichi when she was a child; it's part of why she later developed a crush on him.

Literature

 * Violet wears a hair ribbon whenever she is deep in concentration in A Series of Unfortunate Events.

Web Comics

 * Emily from Misfile wears a headband at all times to cover her widow's peak. Ash tells her she's beautiful without it, but she's not ready to give it up just yet.
 * Played with in this SMBC strip.

Western Animation

 * Violet of The Incredibles goes from hair over face to hair in headband.
 * There's a purple haired emo girl in Scooby Doo: Scare Camp who sweeps her hair back so her whole face shows (although she wears tinted glasses).
 * The Fire Nation crown is in the form of a hair accessory. It's a spiky gold flame and gets stuck in your topknot. There is also drama surrounding an important antique hairpiece in season three, associated with Iroh's revelations about the family.
 * Flashbacks to Ozai's coronation, at which he and his children wore white for some reason, and to the disastrous Agni Kai that changed Zuko's life, feature focus shots on the 'crown.' In fact, Ozai is carefully undetailed in the trauma memory, so that it's only by the outline of the crown (and Zuko's dialogue) you can tell who it is.
 * It's also, obviously, a big deal at Zuko's coronation. Its many differences from his father's (smaller, red robes, integrated audience, crowned by the Avatar instead of a Fire Sage) are very important, but the crown and the standing up are ritually essential and stay the same.
 * Hell, for this trope we don't even need the part where he gets crowned. The third-season adoption of a topknot and release of same before going rogue qualify. Go go Prince Ponytail!
 * Zuko's is a story told in hairstyles.
 * Not relevant, but the reason they wore white was that it was both a coronation and a funeral, and in some Asian cultures you would traditionally wear white to a funeral.