Episode 17 - The Apocalyptic Dragon Chain Cannon

Gray defeats Sugarboy and destroys the key after learning its purpose, as he can create another key from ice. However, Erza Knightwalker captures both Gray and Natsu and brings them before the king, whom she quickly takes hostage, revealing herself as Erza Scarlet. Erza's plan to force the guards to redirect the cannon goes awry when the real Erza Knightwalker appears.