The Eye of Ra is an item from Yu-Gi-Oh! The Falsebound Kingdom, required to Summon "The Winged Dragon of Ra". Only a "Master of Gods" can use it.
The item can only be used once per mission. Once used its gone for the rest of that mission.
It is acquired this by defeating Marik in Joey's storyline. The player cannot use it as Joey, but if they start over as Yugi or Kaiba it will automatically be transferred to their inventory.