Diamond Star

The Diamond Star is the first of the Crystal Stars Mario collects in Paper Mario: The Thousand-Year Door, obtained upon completion of Chapter 1: Castle and Dragon.

Some time after the four heroes sealed the Shadow Queen using the Crystal Stars, the dragon Hooktail got ahold of the Diamond Star and kept it in her castle. During their quest, Mario and his partners traverse Hooktail Castle and defeat Hooktail in hopes of recovering the stolen Diamond Star, as well as to stop her from continuing to terrorize the citizens of Petalburg. Upon defeating her, Hooktail spits out Koops's father, Koopley, who gives Mario the Diamond Star. The Diamond Star also teaches Mario the move Earth Tremor to use in battle.

During the final battle with the Shadow Queen, when the Crystal Stars spread out to the locations as to where they were found, the Star retreats to Petalburg, where its residents, including Koopley, Mayor Kroop and Koopie Koo cheer on for Mario and his team.

Trivia

 * The Diamond Star and the Gold Star are the only Crystal Stars that aren't from a Chapter that involves the X-Nauts or the Shadow Sirens in any way.