Sonic crashes the Tornado into Westside Island, saves Miles Prower or ‘Tails’ from the terrible village.
Sonic finds signs that Robotnik is nearby with his badniks seemingly looking for something. Sonic realizes there is a 7th Chaos Emerald here. Tails actually had the 7th Chaos Emerald, but it got stolen by Robotnik before he could give it to Sonic.
Sonic, with the help of Tails for fixing and even flying the Tornado, get to the Wing Fortress Zone and get the 7th Chaos Emerald to fight the Death Egg Robot as Super Sonic! After the fight, the Chaos Emeralds grow unstable, and eject from Sonic (But they stay close, judging him now that they are fully awakened).
Note: Super Sonic is like Fleetway Super Sonic because the Chaos Emeralds have not properly judged him yet.
The Video Game History Foundation recently put together an absolutely fascinating video on the lost stages of the Sega classic Sonic the Hedgehog 2. It includes partial recreations of some of those cut levels, which have never been seen before. Definitely worth a look!