Pokémon FireRed and LeafGreen/Cape Brink

Now that you have rescued Lostelle, talk to Lostelle's father so you can give him that Meteorite you've been holding. Once that is completed, you can go ahead and sail back to One Island and talk to Bill, who can now link Kanto and Sevii computers!

But wait! Do not talk to Bill just yet! If you do, he'll take you back to Kanto, and you are not done with the Sevii Islands just yet. First, explore Two Island for a great reward.

Move Tutor
In Two Island, make your way north and you'll reach the area known as Cape Brink. Make sure you have your starter Pokemon as the first on your team if you wish to learn its ultimate move.

Enter the only house and you'll meet a very special Move Tutor. This Tutor will teach your starter a powerful attack; if you have Venusaur you'll get Frenzy Plant, Blast Burn for Charizard, or Hydro Cannon for Blastoise. All of these attacks are very powerful, but be warned, their use requires a recharge!

Be aware, the old woman teaches your starter Pokemon this move only once, so act wisely! Traded starters can also learn their respective move even if you have already taught your starter a move, just so long as they are the required Pokemon. When you've chosen to learn this new move or not, check outside all the way behind the house for a Rare Candy.

Now it is time to head to Mt. Ember, and get your hands on the Legendary Bird, Moltres!