Sonic Championship is a fighting game in the Sonic the Hedgehog series. The game's original Japanese title, Sonic The Fighters, is used in North American and European releases of Sonic Gems Collection.
Dr. Robotnik (Doctor Eggman in the Japanese version. His North American name, Dr. Robotnik, was misspelled as "Dr. Robotonic") has built the Death Egg II, along with Metal Sonic. Tails alerts Sonic to this and they plan to fly into space via the Lunar Fox, a spaceship Tails built in an effort to stop it. However, as it is a single seater, only one of them can go and it requires the energy of eight Chaos Emeralds. The two set off in the Tornado to find them, detecting one in Knuckles's possession.
Source: Wikipedia, "Sonic the Fighters", available under the CC-BY-SA License.