Kersti is a Pixl-like sticker fairy in Paper Mario: Sticker Star, as well as Mario's initial companion. She has the ability to "paperize" different stickers in the game, transforming them into objects to be placed in designated locations. During the events of Paper Mario: Sticker Star, Kersti helps Mario retrieve the six Royal Stickers. She initially gives Mario attitude, but starts to soften up as the game progresses. During the final battle, she sacrifices herself in order to defeat Bowser.
Kersti is a friendly and generous sticker, often claiming to be a delicate and refined lady. However, her feisty side tends to stand against this claim, and she's easily angered and tends to make hasty judgments. She treats stickers with respect and gives Mario an album to out his stickers in. As stated in the prologue and Rustle Burrow, Kersti comes from the Sticker Star, and cannot return unless she finds the Royal Stickers. Kersti is shown to have a severe hatred of Kamek being annoyed whenever he appears. In Rustle Burrow, Kersti is stuck in a spider web, shouting for Mario's help. When he rescues her, she yells at him while unaware that Mario had lost his album but quickly apologizes.
- Kersti's name is a spoonerism of the word "sticker" but with the letter C removed. The letter C may represent the Crown shape of Kersti.
- Kersti's appearance is very similar to a Pixl From Super Paper Mario.
- In both areas where Mario loses Kersti, you are unable to Save or return to the World Map. This is possibly so you can't go to other places without Kersti.
- Kersti seems to take the role of every partner/pixl in the paper mario series, as she has multiple abilities.
- With powerful stickers, it's possible to beat Bowser without ever using Kersti. She will still remain in the album after the battle and can be tossed like any normal sticker however it is unknown how she would be used otherwise as Stickers are not saved after the credits.
- At first, Kersti will be mad at you. she thinks Mario touched the sticker comet. Once Mario explains, she thinks Mario put the blame on someone else. She calms down after Mario says he was going to help.
- Kersti has a personality nearly identical to that of Starlow from Mario & Luigi: Paper Jam.
- Kersti slightly resembles Rosalina's crown, both are silver and have turquoise gems on both sides.
- In the final battle after using Kersti as a sticker, it is impossible to not get a jackpot on the modified battle spinner. The spinner will still offer the upgrades for double slot alignment and slowing down the aligned slots, but these do not matter as you will always get a jackpot regardless.