The Trap of Father and Child (Chichi to Ko no Wana- 父と子の罠) - S1.E14

Voltes rescued an airplane piloted by a man which turned out to be a runaway slave. But after the man was brought to Big Falcon and treated, he sneaked into Voltes hangar and sabotaged Tenku-ken, he betrayed Voltes because he was promised by Heinell if he did so, his daughter will be given to him. Heinell lied and Voltes had to face the enemy with the mighty sword, Tenku-ken, nailed to his chest.