The English story prologue found in the original western manuals:
Save Floating Island!
The last time Sonic and Robotnik went head-to-head, Sonic blasted Robotnik's Death Egg to smithereens. The explosion heaved Sonic deep into Floating Island's Mushroom Hills!
Sonic knows that many emeralds, including the Master Emerald, are hidden somewhere on Floating Island. He bets this Knuckles character knows where they are! Sonic can't let Robotnik get his hands on the Master Emerald. He'd have Death Egg fuel forever — and Floating Island would be destroyed!
Now Sonic's got two problems. How to protect the Master Emerald? And how to keep Knuckles off his back? He'll have to deal with that wild Echidna right away!
Knuckles has problems, too. As guardian of Floating Island and all the emeralds, Knuckles has a mission: to wage war on all invaders. Whoever threw that bomb is in DEEP trouble. Knuckles is ready with tricks, traps, and bare-fisted attacks to keep Floating Island safe.
Sonic's not taking any chances. Neither is Knuckles! But while they're going the rounds with each other, who's stopping Dr. Robotnik? Could this be the end of Floating Island?
A translation of the story prologue from the Japanese manual:
Dr. Eggman's large fortress, the Death Egg, was going to escape into space, but Sonic crashed his 'Egg into the ground again. As he escaped from the falling space station, Sonic was thrown down by the wind and into the "floating island", where huge mushrooms grow luxuriantly inside a deep forest.
The Death Egg's safety was confirmed as it crashed into into the large volcano of the "floating island". Sonic was annoyed that the Death Egg had survived and would not feel totally at ease, unless it was completely destroyed. Sonic realizes Dr. Eggman couldn't complete the Death Egg properly due to the amount of time he had to work on it!
Just as Sonic ponders this, Knuckles appears from the door hidden in a thicket, and looks around cautiously. After a quick look, he ventures out and disappears into the wood. Sonic waits for Knuckles to disappear, and then pushes a button to open the door to the room. As he enters the room, Sonic is astounded by a dazzling bright light, that seems to reflect in his eyes. The light came from the special shining "Super Ring".
"What is this ring?"
Sonic couldn't tear his curious eyes away from this shining ring. He thought the ring was wonderful, but the moment he touched it with his hand, Sonic heard a shrill sound and was catapulted across the dimensions.
When Sonic arrived on the other side, he ended up in a large room he had never seen before. Sonic found it odd that the solemn altar that was built into the large room had not collected dust at all. Just as Sonic looked up at the large altar, he faltered in surprise. In the center of the altar, sat the "Master Emerald", a huge deitied Chaos Emerald.
What is up with this strange altar?
Just what does this Knuckles guy do here?
This island has a massive secret and Sonic bets that Dr. Eggman knows what it is!
But Sonic will have to face Knuckles in a final confrontation in order to get to him!
The "Sonic the Hedgehog" adventure on the "floating island" is underway and there is still more to come!