Born Ryusei Chisato, he was the child of two scientists of nearly supernatural intelligence. His parents were murdered, but he was saved by his companion, the shapeshifter Garo. He was raised by his foster parents, the Kaguras. Tatsuo spent his life searching for his parents' murderer, to take revenge. He discovered that it was his grandfather, Kogetsu Chisato, who had his parents. Chisato then set fire to his mansion, intending to kill himself, Tatsuo, and Tatsuo's sister Maya. Tatsuo survived, and continues his battle against crime and corruption.