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Well, it's very hard to say either way, because KH is very very unclear as to exactly how a keyblade is created. And without that vital piece of information we can't determine if Riku's keyblade was made the "natural" way or not. Who knows? Maybe all keyblades are created through the fusion of several strong hearts? Although, after KH2, that theory is kind of smashed to pieces with (spoiler) Kairi's keyblade!

I find it impossible to call any of the keyblades "real" or "fake" until we know what defines a "real keyblade".

Now, on the less technical side, I find Riku's possession of the "Way to Dawn" keyblade to be a wonderful plot device and I great way to further characterize Riku. Sora's keyblade is able to unlock things and get a glimps at what lies inside them, much like his cheerful and compassionate personality. Riku's on the other hand allows him to lock/unlock people's hearts, much like he himself does. You see it all the time in the game; Riku meets Sora, and no matter the situation, knows exactly how to get under his skin, how to get past his "good guy" exterior and talk to the inner Sora. (ie. the less selfless Sora who's lost and worried about his friends)