Lost Key

Lost Key is the fourteenth episode of Tenkai Knights. It first aired on November 23, 2013 on Cartoon Network in the United States.

Plot
Vilius and Dromus have successfully kidnapped the Tenkai Dragon. On Earth, a stranger returns to Benham City. Meanwhile, Guren and the others try to figure out their next move.

On Quarton, Vilius revives Slyger and Granox. Vilius and Dromus then go to inspect the captured Dragon. On the way, Vilius warns Dromus that the Tenkai Knights are not who they claim to be. Dromus agrees, while slyly implying that he secretly wishes to usurp Vilius's command.

Back on Earth, Guren and the others are still trying to come up with a strategy to rescue the Tenkai Dragon. When they can't come up with anything, they agree to meet up again at the Shop of Wonders to try once more.

Back on Quarton, Dromus prepares to enact a plan to ensure the Tenkai Knights will be to busy to attempt to free the Tenkai Dragon. Once he leaves, Vilius ponders how to gain control of the dragon, and comes to the conclusion that he must find the Black Dragon Key.

Back on Earth, Guren wonders if Dromus is a greater threat than Vilius when he runs into Gen. Gen asks to talk with Guren, so Guren invites him to his house. Gen gives Guren his coin, telling Guren he figured he'd give it to him since he seemed so interested in it before going home.

The next day after school, the boys go to Quarton, where they discover Beag and his men surrounded by some Corrupted soldiers. The Knights upgrade to Titan Mode, but are attacked by Dromus. When Dromus attempts to finish Bravenwolf, the others overwhelm him and he orders a retreat.

After the battle, Guren and the others return to Earth, disappointed with their performance despite their victory. While on Quarton, Vilius curiously studies the information downloaded from Toxsa's mind about Earth.

In the episode

 * Gen gives Guren the coin he showed him in "Two Sides to Every Coin" to keep.
 * Beni appears for the first time at the end of the episode and reveals she possesses a core brick.
 * The second Japanese ending theme is first featured on this episode.