Kersti

"As their caretaker, it's my duty to find all of them, or else I can't return to the Sticker Star!"

- Kersti

Kersti is a sticker fairy who appears in Paper Mario: Sticker Star. Kersti grants Mario the ability to use the Battle Spinner and paperization. She is Mario's initial companion in the game, and his only companion for the vast majority of it. Kersti's name is an anagram of the word "sticker" but with the letter C removed.

History
According to her introduction, Kersti came from the Sticker Star on the night of the Sticker Fest, as part of the process of granting everybody's wishes. Kersti first meets Mario at the site of the Sticker Fest, stuck to a sign after Bowser destroys the Sticker Comet and steals one of the Royal Stickers for himself. After Mario peels her off, Kersti goes off on him, believing it was he who destroyed the Sticker Comet, but after Mario offers to help search for the Royal Stickers, she forgives him, and they set off to find the six Royal Stickers.

At the end of their adventure, Kersti sacrifices herself in the final battle with Bowser, allowing Mario to use her as a sticker to increase his power and overcome the power granted to Bowser by the last Royal Sticker. However, after the battle, Mario brings Kersti back to life by wishing on the Royal Stickers. Having returned to the site of the rebuilt Sticker Fest, she scolds Bowser for trying to steal the Sticker Comet again. She then jokes about changing her career, and Mario, Peach, and Bowser laugh.

Personality
Kersti is shown to be benevolent, but also has a feisty side to her. She has an aggressive dislike of Kamek.

Powers and Abilities
Kersti has the ability to "paperize" stickers by pressing, turning the stickers into objects that can be placed into designated locations. She also has the ability to create a tool used during any battle she is present in called the Battle Spinner; this is a slots-type minigame where Mario must match up two or more images in order to use more stickers per turn, and if Mario gets three of the same image, a special effect will occur.

Like Goombario and Goombella before her, she can give area tattles (by pressing ), but not on enemies. Thus in certain scenarios when Mario is separated from Kersti, he can't use these abilities. In the final battle with Bowser, Kersti sticks herself into Mario's album, and when used by Mario, creates a special battle spinner that always wins by landing on her image. Mario is slightly healed, and 5 sticker slots are created which do not diminish after a turn. Then for the rest of the battle, Mario becomes shiny, allowing him to do normal damage to Bowser despite his Royal Sticker.

Sticker Description
"Sacrifices herself to give Mario all her power, leaving everything to him."

Trivia

 * Kersti slightly resembles a Pixl from Super Paper Mario.
 * In both areas that Mario loses Kersti, the player is unable to save the game or return to the World Map. This is most likely so the player can't go to other places without Kersti.
 * With powerful stickers, it is possible to defeat Bowser entirely without ever using the Kersti sticker. She will remain in the album after the battle and can be tossed like any other sticker. However, it is unknown how she would be otherwise used in the game, as stickers are not saved after the credits.