Spirit Keys
Spirit Keys are items created by Kagemaru along with the Spirit Gates as a means of getting high-level duelists to duel each other in order to generate the duel energy necessary to revive the Sacred Beasts.
Kagemaru said that they were unnecessary to open the gate. Sheppard gave one key to the seven top duelists at Duel Academy: Chazz, Bastion, Jaden, Alexis, Crowler, Zane, and Banner.