Leo and Luna's custom Disks are customized Duel Disks used by Leo and Luna
Leo and Luna's Duel Disk were originally blue and pink versions of the 5D's standard Disk. However these were too big for their arms and could easily slip down while in use.
After Leo and Luna were visited by Yusei Fudo, Yusei observed how Leo's kept slipping during a Duel, so he customized the two Disks to fit them better before leaving.
In Yu-Gi-Oh! 5D's World Championship 2009: Stardust Accelerator the player can unlock Leo's custom Disk by defeating Leo and Luna ten times in Tag Duels and Luna's by ending three Duels in a Draw.
In Yu-Gi-Oh! 5D's World Championship 2010: Reverse of Arcadia the Duel Disks are unlocked in the same way as Stardust Accelerator, but the player need only get a Draw in three Duels.