Kagato is the former assistant of Washu Hakubi, the greatest scientific genius in the universe, assisting her in the creation of her daughter Ryōko, her battleship Ryo-Ohki, and in the building of the massive battleship, Sōja.
Kagato has largely the same superhuman abilities as Washū and Ryōko, though whether he was born with these powers or achieved them by genetically altering himself was unclear until the release of the True Tenchi Muyo! Kagato caught word of a historical artifact, one said to hold the "greatest energy in the universe." Ambitious with an amoral curiosity, he imprisons his mentor within her own ship, taking credit for her creations, taking Sōja for his own, and using it to pillage the galaxy (Washū would remain in his captivity for the next five thousand years).
Those caught in the collateral damage of his "scientific methods" are similarly out of luck.
Having a powerful psychic hold over Ryōko through the gems, which are her energy source, Kagato uses her as his puppet to execute his orders, sending her on archaeological excavations as he scoured the universe for hints on his own.
Once observed, a location would be razed - whether it be populated or not - lest someone else replicate his research.
In all, 3,326 ruins were destroyed, with great loss of life and innumerable cultural artifacts stolen.
He is fascinated when Ryōko intervenes, wondering what she could ever see in the boy.
Kagato reasserts his control over Ryōko (Kagato's control manifests itself in Ryōko's eyes; when she possessed all three gems her eyes glowed red, but with only one gem the whites of her eyes became light green, the same color as Kagato's sword) and has her take Tenchi hostage as he interrogates; Ayeka, Sasami, and First Class Detective Mihoshi Kuramitsu stand by as Kagato wonders if Tenchi is aware of the sword's power and whether the boy is suitable to unlock it.Tenchi is able to break free from Ryōko's grasp and attacks, but does nothing but nick Kagato's cheek (which quickly regenerates, but not before drawing greenish blood).Angry, Kagato engages the boy in swordplay to test him, and is sorely disappointed by the result.It was during this time Kagato earned the name "Ruins Buster" and a place on top of the Galaxy Police's Eternally Wanted List.Slaves under a ruthless space pirate, Ryōko and Ryō-Ohki were recognized as major threats themselves.Eventually, Kagato found the power he was searching for was linked to the imperial planet Jurai and its Royal Family bloodline, and Ryōko was sent on an errand to retrieve it.