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You go back to traverse town and talk to both cid and leon
You get it after clearing Deep jungle. Cid installs it after you get earthshine from Leon in Traverse town
Return to Traverse Town. You will need to occasionally revisit Cid so that he can improve your Gummi Ship.
In the fist Kingdom Hearts, Cid is located in the Item Shop across from the main square in Traverse Town. He works the register at the Item Shop. In Kingdom Hearts 2, Cid is with Squall (Leon), Aerith, and Yuffie. He is the "tech support" of the group.
You know the place where Leon took Sora when you fought Leon? When you were supposed to follow him, you went to a place where there was a little stream of water. Walk through it and use Trinity on the gate.
They believe in the heart of the cards.
There are no guns in Kingdom Hearts 358/2 days unless you are preferring to Leon
So far, not in any Kingdom Hearts games, but maybe in the future Square Enix will allow that function in Kingdom Hearts III.
Traverse Town is a collection of tiny bits of worlds that have been destroyed, brought together to make a single world. It is where people whose own worlds have been destroyed often wind up. People such as Leon, Yuffie, Pinocchio, and Gepetto take solace here.
In Hallow Bastion in Kingdom Hearts, Merlin is a wizard from The Sword in the Stone, a Disney film, who lives with Aerith, Cid, Leon, and Yuffie.
Leon is a side character that appears in most of the Kingdom Hearts games. His true identity is Squall Leonheart, the main character from Final Fantasy VIII. In the first Kingdom Hearts game Yuffie (another side character, originating from Final Fantasy VII) calls him Squall, but is quickly rebuffed, as Leon tells her he no longer goes by that name. It is not explained why, however.
Because Leon is in his early 20's, and Birth by Sleep takes place 10 years before Kingdom Hearts 1, Leon will only be about 10 or so, if he does indeed appear. Therefore, he will be Squall, not Leon, and probably will not have a big role in the story, if any.