Sushie is a Cheep-Cheep who lives in Yoshi Village on Lavalava Island. She is Mario's seventh partner in Paper Mario, and has a daughter named Sashimie, who sends her a letter at one point and is never seen in the game.
Sushie told the five Yoshi kids, the Fearsome Five, to not go into the Jade Jungle due to the evil beasts inside. However, they tricked her and trapped her inside a tree, and ran into the Jade Jungle. Mario got Sushie out of the tree and she joined his party to find the kids. Eventually they found all five of them. The Yoshi chief gave them a Jade Raven to get to Raphael Raven so they could enter Mt. Lavalava. Initially Sushie disapproved due to the dangers of the volcano, but upon hearing that Mario wanted to rescue Princess Peach from Bowser, decided to travel with him until the end. They entered Mt. Lavalava and rescued the fifth Star Spirit, Misstar, after defeating Lava Piranha.
Following this, they made their way through Flower Fields and Crystal Palace to save the last two Star Spirits, Klevar and Kalmar, and then reached Bowser's Castle. One room was full of water, through which Mario traveled using Sushie's ability. Eventually they defeated Bowser and took the Star Rod back from him.
Afterward, Sushie returned to Yoshi Village, and all the monsters in the Jade Jungle were now gone. Sushie also received an invitation to a party at Peach's castle.
Sushie's ability outside of battles is to travel through water with Mario whenever they are standing on a dock, and can also dive down to get items and coins underwater.
In battle, Sushie's abilities are:
Tidal Wave will make the battle with Lava Piranha much easier.