The Master Key used by the Juraian Royal Family
Tenchi-ken is the sword wielded by Yosho and later discovered by Tenchi when he stumbles into Ryoko's cave. Appearing to be just a plain blade-less sword hilt, Tenchi-ken is a sword whose blade is manifested by the Juraian energy harnessed by its wielder. As a result, only those who are descended by the Juraian emperor are able to touch the sword and anyone not Juraian that tries touching Tenchi-ken will be rejected by it with a painful electric shock. The sword also functions as a "master key" giving it the capability of controlling all royal trees, except for the origin ship, Tsunami.
Yosho had used Tenchi-ken to extract Ryoko's gems before sealing her up in the cave and are found fused to the hilt of Tenchi-ken. It is possible for the sword's wielder to transfer the gems back to Ryoko as Tenchi concentrated his Juraian power early in the series to transfer one of Ryoko's gems back to her.