What does Sora use when riku takes his keyblade?

the concept of keyblades is a complicated matter. Especially when it comes to Riku. To answer the main question. I will put it simply. As shocking as it may be, Riku is actually the real Keyblade Master. Yes it is shocking but it has been referenced several times. Riku tells Sora directly but he doesn't believe him. After you beat the first visit to Hollow Bastion, Jiminy will write it in his journal. Even in Birth by Sleep, Ventas, Terra, & Aqua receive a prophecy that it will pass on to Riku & they even perform a ritual to ensure it. With all this, most people wonder why the Keyblade didnt go to him in the start. Well it was actually supposed to. The tutorial level (Awakening) was a dream that Sora had but Riku was the one who was supposed to have it. When Riku chose to open himself to darkness, he cast aside his destiny. Sora, my touching him, escaped from the darkness, and thanks to the pureness in his heart, the weapon passed on to him. However, Riku still maintained the power the keyblade bestows. This allowed his power with the Soul Eater Keyblade, and eventually let him claim the Kingdom Key from Sora. In Kingdom Hearts 358 over 2 days, Riku is able to pick up Xion's keyblade, however, it being fake, anyone could do it. Even someone who'd never held a keyblade before. However, the question is also posed why he stole oblivion from Roxas in their fight at the alley of naught. This is simple. The keyblade is linked to the heart. Without a heart, nobodies cant retain even thier own weapons. Sora is the only keyblade master who can call back the keyblade to him. Roxas & Xion can't. That is also why Roxas (Faded Memory) was so suprised when Sora summoned it back in the Station of Serenity fight. Finally the question of Sora and Riku being able to hold each others keyblades in the fight against Ethereal Xemnas. Though this is partial to the rule that keyblade masters can temporarily weild each others keyblades, it mainly is because Riku & Sora share a bond with the ONE KEYBLADE that rules them all (Sora's) and thus maintain a sort of combined power. This is why Sora and Riku both touched the keyblade to shoot that beam through xemnas. In order to access the complete power of the one keyblade both Sora and Rikus power are needed. On a final note, Riku's once dark keyblade (Soul Eater) is transformed into a balance of light & darkness (Way to the Dawn) This is a symbol of Riku casting aside the darkness and embracing the true light within himself. It is marked by Roxas rejoining Sora. As the end of one being that balances light and dark, so begins a new one.