Rathie

The Kurumizawa guy is an unnamed Yu-Gi-Oh! 5D's character who works in the Kurumizawa store.

Biography
He helped Carly inestigate the Crimson Dragon appearance at the Fortune Cup, y researching the Signers. Knowing Carly would want to contact Akiza, he also dug up information on the Arcadia Movement, which he wasn't willing to give her for free. To his delight, Carly gave him a rare Dark Magician Girl figure in exchange for the information.

Non-canon appearances
In Yu-Gi-Oh! 5D's Tag Force 4, he works in the Kurumizawa store, where he sells Booster Packs to the player.