The Key to Evil

The Key to Evil is the eighteenth episode of Tenkai Knights. It first aired on January 11, 2014 on Cartoon Network in the United States.

Plot
Beni meets with Guren and the other boys just as school gets out. Guren introduces her to the others and she tells him she wants to show him something. She takes them to the docks and reveals that she'd tricked them. The boys are temporarily rendered unconscious. When they wake up, they realize they'd been transported to Quarton.

Another Guardian, calling himself Eurus, appears before them and tells them that they are about to take a test. The Knights have to battle evil clones of themselves created by Guardian Eurus. Meanwhile on Earth, Gen begins to get suspicious of Mr. White.

The Knights manage to Titan Fusion and Bravenwolf and Tributon destroy all the clones. Beni is surprised that the boys won and realizes she shouldn't underestimate them. Later, Gen, as Dromus, and Eurus meet and talk about how to use the Tenkai Knight's Titan Fusion to find the Black Key. While Gen is suspicious of Eurus's motives, the Guardian claims to be helping Gen to keep balance because Boreas is helping the other Knights.

In the episode

 * Guardian Eurus appears before the Tenkai Knights for the first time.
 * It appears Guardian Eurus is the one who gave Gen and Beni their cores and is responsible for their being on Quarton, like the boys and Guardian Boreas, but that is not confirmed.
 * The Knights (Bravenwolf and Tributon) unlock and use Titan Fusion for the first time.