Sonic the Hedgehog has a new partner, Blaze the Cat, in this fast-paced platformer, Sonic Rush. You can play as either Sonic or Blaze as you try to track down powerful Sol emeralds. Sonic Rush displays the level over both screens, allowing for screen-spanning jumps and dives. Some gameplay modes include stylus support as well.

Designed as a 2.5D side-scroller, Sonic Rush is the first game in the Sonic series to explore both 2D and 3D venues by combining two-dimensional environments with three-dimensional models. In 2007, the game received a sequel, Sonic Rush Adventure.

At the beginning of the story, Blaze the Cat, an antisocial princess from an alternate dimension, appears on Sonic's world. Her world had the seven Sol Emeralds—gems similar to the Chaos Emeralds—which it relies on for survival. However, they were stolen by Dr. Eggman and as Blaze was chasing him, a light brought her to this world. Blaze then makes it her goal to personally retrieve the Emeralds from Eggman. Upon finding Eggman, the doctor flaunts a Sol Emerald, stating that he needs them to access ultimate power. Enraged, Blaze defeats Eggman and regains the Emerald. Though Eggman escapes, Blaze is determined to get the rest.

Confused and alone, Blaze ponders how she will get the Sol Emeralds back, and how to return home. She soon spots Cream the Rabbit and Cheese hiding in the bushes, and is surprised by Cream's politeness, the young rabbit eager to make friends with Blaze. Brought to Cream's home for a cup of tea, Vanilla and Cream convince Blaze to have the latter be her local guide after hearing her story. However, Blaze dismisses their advice to seek Sonic's aid, believing she can do this alone. Despite having Cream tag along, Blaze remains mostly indifferent to the young rabbit's efforts to be her friend.

Elsewhere, Sonic encounters Eggman during a run, who boasts about how he will soon have ultimate power. Upon defeating Eggman, Sonic finds a Sol Emerald that Eggman dropped, at which point Blaze appears and reclaims it, thanking Sonic for defeating Eggman before leaving. Confused, Sonic teams up with Tails to figure out what is going on while collecting the Chaos Emeralds.