The first 29 episodes adapt the rest of the 24th volume through the beginning of the 25th volume as part of the "Sirius Island" (天狼島編, "Tenrojima-hen") arc, which focuses on Natsu and the guild's other strongest members as they take their S-Class examination on Sirius Island, they are interrupted by the arrival of Grimoire Heart, who attempt to retrieve the dark wizard Zeref living on the island. Next 25 episodes features a completely original, self-contained story arc called "Key of the Starry Heavens" (星空の鍵編, Hoshizora no Kagi-hen), and focus on Natsu and the members of Fairy Tail as they meet a relative of the Heartfilias', and face a religious sect of warriors and a revived Oracion Seis as they try to find the parts to an ancient doomsday weapon.