Lore Regarding Dual Wielding Keyblades

[Raybrand]

For fanfic reasons how does one come to wield dual keyblades? Can some keyblades manifest in pairs, I've read somewhere that Roxas was able to dual wield because one of them wielded sora's keyblade and the other wielded ventus's and when xion fell roxas gained the other keyblade, then when he rejoined with sora he gained that ability.
If this is accurate then dual wielding keyblades only occurs under rare and unusual circumstances but is there any lore to support the ability to wield two keyblades naturally?

Edit: Apparently Sora cannot dual wield in kh3 I don't know what that means for his connection to Ventus or just a gameplay mechanic change

 

[Zettaflare]

I believe Nomura stated you need to posses two hearts in order to duel wield. The reason Sora and Roxas can is because they each had Ventus' heart along with their own

 

[Absent]

Roxas wielded Sora's Keyblade for one year. The trauma of Xion's death allowed Roxas to tap into Ven's Keyblade later on. While you don't get 2 Keyblades for one heart, you could technically use keyblade transformations to turn one keyblade into two weapons(not into separate Keyblades) as seen with Lingering will and KH3 Sora.

 

[Zettaflare]

Just realized if it wasn't for lingering will Terranort could have dual wielded as well. He had both Terra and Xehanort's heart

 

[Luxu]

Sora has Ventus' heart within him, allowing him to use both his own Keyblade as well as Ven's.

Roxas had that ability because Ventus' heart was within him, as well as using Sora's Keyblade. After Xion's death, the grief Roxas had from it summoned Ven's Keyblade. By theory, Sora inherited that ability from Roxas. So unless your O.C has a second heart, by Kingdom Hearts logic he/she can't duel wield.