We found out that Riku's Keyblade's name is "Way to the Dawn" when examining his item slots after he joined your party. Is that Keyblade a transfigured version of Soul Eater?
I designed it with that image. Since Riku has always been using Soul Eater, he still calls it that even after it changed form. Keyblades aren't something that you can obtain suddenly out of nowhere so in Riku's case, his Soul Eater was used as an intermediary for that Keyblade.
If we directly translate "Way to the Dawn", "dawn" means "in-between night and daytime", so does that mean that Keyblade is from the In-between World? In other words, this means the Keyblades that Sora, King Mickey and Riku wield represent the Worlds of Light, Dark and In-between?
Well, if I have to say where they belong, it's just as you said. But the name of "Way to Dawn" doesn't have to mean that. This name came from the scene at the end of Riku's story in KH:COM that suggested which path he would walk on, where he said "The road to dawn."