From the Super Mario Wiki
Twink is a Star Kid in Paper Mario. He is a star that helps Princess Peach in her time of need when she gets kidnapped by Bowser. He frequently gives Mario and his partners information on where the Star Spirits are being held captive. He was born in Starborn Valley. He was then ascended to Star Haven immediately after Bowser stole the Star Rod. If he had ascended any earlier, he would have been trapped there and unable to assist Peach throughout the course of the game. Some dialogue from the other Star Kids still in Starborn Valley suggests that he had somewhat of a big brother relationship with the others and looked after them when he still lived there.
When Peach is first captured, she wishes for help, and Twink arrives. Since he is so young, he isn't able to grant any big wishes. He can, however, assist Peach in eavesdropping around her castle.
After Mario and Goombario goes to Shooting Star Summit, Peach asks Twink to carry the Lucky Star to Mario and tell him that she is fine. Twink recognizes the Lucky Star. When Mario heads back for Toad Town, Twink knocks into him. He keeps saying sorry but turns happy recognizing Mario. He gives Mario the Lucky Star, and asks him if he wants an Action Command lesson. Then he tells Mario that Peach was fine and leaves. Goombario comments that he is brave.
After Chapter 1, Twink and Peach find Bowser's Diary which reveals the second Star Spirit's location. Princess Peach asks Twink if he can tell Mario about it, and Twink agrees. When Mario returns to Toad Town, Twink greets him, praises his work on defeating Koopa Bros., and tells him about Mamar's location.
After Chapter 2, Twink is hiding behind a wall when Bowser is talking to Peach. He hears Bowser talking about the "Invincible" Tubba Blubba, and suggests searching for the information. They sneak out and hear in the library of Peach's Castle that Tubba Blubba has a weak point. However, Mario already defeats Tubba Blubba before he figures out what it is.
After Chapter 3, when they are trying to sneak out, Twink hears from Bowser that Mario's next destination would be Shy Guy's Toy Box. When Mario goes to the west of Toad Town, Twink finds him, praises his work on defeating Tubba Blubba, and tells him about Shy Guy's Toy Box.
After Chapter 4, when Peach is going to cook something for Gourmet Guy, they come to the kitchen in the castle. Twink picks a cookbook in the bookshelf in the kitchen, and suggests "Special Strawberry Cake". Peach agrees and Twink reads the instructions for Peach. Eventually Gourmet Guy enjoys the cake and tells Peach about the fifth Star Spirit's location. Princess Peach asks Twink to tell Mario about it, and Twink once again agrees. After Mario rescues Muskular, Twink comes and, seeing Muskular, calls him "the honorable Star Spirit". Muskular recognizes Twink and he says he is touched. After Muskular goes up to the sky, Twink tells him about Misstar's location.
After Chapter 5, when Peach is discovered by Mr. Hammer, Twink is frightened and hides behind a vase. When Peach is taken to 64th Trivia Quiz-Off, he followed Princess Peach as she participates in the show.
After Chapter 6, Twink suggests using the Sneaky Parasol Peach gets from Mr. Hammer, and follows her as she proceeds.
After Chapter 7, after the Koopatrols tie Peach up, Twink tries to attack the Koopatrols but is knocked out of the castle.
When Mario and his partners fight Bowser, Twink decides to take on Kammy Koopa. When Twink is fighting, he can only use Dash, while Peach can increase his Attack Power with her wishes (expressed as Focus). Once Kammy is defeated, Mario is given the upgraded version of the Star Beam, the Peach Beam, in which Twink assists the other Star Spirits, making it possible for Mario to defeat Bowser.
At the end of the game, Twink bids farewell to the princess, telling her he's going to make people's wishes come true. It seems that Twink wants to tell the Princess something further, but he stops himself and rises up to Star Haven.
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