Voltron: Defender of the Universe: The Complete Series
Voltron: Lion Force, The Missing Key
S1 E4:
Keith and the team uncover the key to the Black Lion, just as King Zarkon's Robeast is about to rain havoc on Planet Arus. Together, they are able to form Voltron's most powerful weapon, the Blazing Sword! But the battle leaves Sven uncertain about his role as a member of Voltron Force.