Yu☆Gi☆Oh! Duel Monsters GX

Synopsis

Jaden, Chazz, Bastion, Zane, Alexis, Banner and Crowler are all summoned to Chancellor Sheppard's office. The Chancellor explains to them about three legendary powerful cards, the "Sacred Beasts", that were sealed away underneath Duel Academy. He says that an evil group called the Seven Shadow Riders are planning to unseal them and use their power. He gives everyone one of the seven "Spirit Keys", which have the power to unlock the seal, and tells them to protect them from the Shadow Riders, as the keys only have power when won from their guardians in a duel. It doesn't take long for the first Shadow Rider, Nightshroud, to appear and challenge Jaden to a duel for his Spirit Key in exchange for Syrus and Chumley's lives. Plus, if Jaden loses, he will have his soul sealed inside a card.

(Source: Wikipedia)