Tenkai Dragon Cube / Secret of the Tenkai Dragon

S1 E2: After their first trip to Quarton, Ceylan refuses to return to Quarton. During a visit to the museum, the two boys see an ancient stone tablet that later turns into a key in front of them. After this event, they are summoned to go back to Quarton, where they meet Granox and Slyger, two of Vilius' most powerful warriors, while Lydendor and Valorn join the fight, getting the first Dragon Cube.