Ciela

Ciela is the first Fairy Companion who helps Link in Phantom Hourglass.

True Identity
She first meets Link when he lands on Mercay Island and takes him to her "grandpa", Oshus. Eventually she and Link begin to travel together along with Linebeck, whom she doesn't like much and often fights with.

After beating the Temple of Courage in Molida Island, however, instead of a colorful fairy, another white fairy much like Ciela appears. Link goes to Oshus, who also has traveled to Molida during that time, and uses his staff to fuse the new fairy and Ciela together, revealing that she is in fact the Spirit of Courage, and whose true color turns to be yellow.

Prior to the game's beginning, Ciela had split herself in two to prevent Bellum from sealing her away like he had with the other spirits.

Abilities
By collecting 10 Courage Gems and offering them at Spirit Island, Ciela can allow Link the ability to perform a Sword Beam. Collecting 20 gems doubles the width of the beam.

In the final boss fights, Ciela provides Link with Phantom Spheres, allowing him to temporarily freeze time. It is around this time that Ciela fully regains her memory as Spirit of Courage and Time. The final scene before the credits is Ciela saying her goodbyes to Link and Linebeck. She eventually gains respect for Linebeck as he does for her, and is sad to see him go.

Phantom Hourglass manga
In the, Ciela plays a role nearly identical to the one she plays in the game, with one exception: Ciela's lost memories take on the form of a mysterious girl. Link and Linebeck first encounter her on the Isle of Gust. Link comments that she seems like "an empty shell" and Linebeck warns him that she might be a threat to them. However, the girl is soon attacked by Crayk and Link departs to Molida Island to rescue her. Once Link has defeated Crayk, the girl responds by thanking them. Link expects to see the Spirit of Courage, but Oshus appears and tells Link that she is already there. Link turns to the girl and asks if it is her, but Oshus tells him that she isn't the Spirit. He then tells Ciela that he's "sorry that he hid the truth for so long" and Ciela's memory rejoins with her, creating the Spirit of Courage.

Trivia

 * During the final battle with Bellum, Link cannot use the Sword Beam due to Ciela's capture at the hands of Bellum.
 * Ciela is similar to cielo, the Spanish word for "sky" (although the name can also connotate "heaven"), which is appropriate given the nature of Ciela's character to fly around the screen. Her name is also appropriate considering courage is frequently associated with the element of wind, such as Farore's Wind as well as Link's role in The Wind Waker.
 * Ciela is depicted with three colorations: white at the beginning of the game, yellow after her true identity is revealed, and blue on official artworks. Ciela's yellow color is unique because the color signifying courage is typically green in the Legend of Zelda series.
 * Because the voice acting used for Ciela in the game is taken from Navi from Ocarina of Time, and early trailers for the game featured the fairy speaking yet did not show Ciela's name, many fans initially believed she was Navi.
 * Ciela bears resemblance to Tatl of Majora's Mask, due to the yellow color she takes when revealed to be the Spirit of Courage. The Spirit of Healing from Spirit Tracks bears resemblance to Ciela's first form, due to her white color.
 * Ciela shares some similarities with Tippi, Mario's Pixl partner in Super Paper Mario. Both are fairies (a fairy-like creature, in Tippi's case) who were injured, had their memories wiped, and were eventually found and taken in by old men with magical powers - Oshus and Merlon, respectively.