In some form or fashion Tenchi's sword is introduced in each of the series. The sword was used to remove the three gems from Ryoko whom was placed in a shrine to keep her imprisoned forever. When Yosho's daughter Achika had a little boy she named him after this sword. By the time Tenchi finds the sword 700 years later the blade is rusted and breaks immediately after being removed from the scabbard. The power of the sword stays intact. When he strikes the rock that was nearby, the rock splits in half. This opens the cave to where Ryoko is imprisoned and still recovering from her battle. Held within the hilt of the sword are the three gems. The power of the gems awoke Ryoko herself.
Tenchiken (The Japanese name for the sword) is also known as "The Master Key". The reason that it is called this is that it was Yosho's control mechanism for this Spaceship Tree, Funaho. Tenchiken, like other spaceship keys comes from the branch of a tree of Jurai. Usually the key is from the tree which it controls. The shape of the key depends on the user. For example Ayeka's key is her tiara. Since Yosho was to become the King of Jurai he received a key from Tsunami, the first spaceship tree. This key can operate all other spaceship trees like a master key hence its name. Since Yosho was a master swordsman trained in Jurian Martial Arts the sword took the form of a Light saber-like sword with incredible power. Then again just about any part of Tsunami contains tremendous power. Tenchiken could be a blender which would kick you ass.