In the kingdom of hearts game one. How do I get the supper key?

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Hope this gets me best answer!! ; )

to get the keyblade, finish the second requirement for kairi in destiny islands

then some cutscenes then heartless will appear. you are currently with a wooden sword so you can't kill them yet

go to the small island connected through a bridge then you will find riku standing there. then he will be sucked by the darkness.

then the word "keyblade" will appear on the screen many times.

then you have the keyblade. you can now kill heartless.

then go to the secret cave in the island to continue with the story

XD