Yukinojo

If Kain was being tactical, then not only he attacked the GXP to prevent them from stopping him, he also stole info on all Jurai lineages from their databases: past and current and covered his tracks. He would have obtained all the necessary info from them and known who to attack to eradicate all who could pose a threat to him. Tenchi and the gang is THE force to oppose after saving the Jurai Empire from an imposter, escaping and fighting Jurai forces and the GXP along the way.

Being imprisoned for a hundred years in the space time prison made with the GXP and Jurai might combined would have taken a lot of Kain’s energy just to break out of. Kain took a beating before being imprisoned and probably slowly forced his way out of the prison, his energy must diminished some which would explain why he only went back to Tokyo, Japan 1970 instead of Jurai thousands of years of ago before the first emperor. Washu had a bit of difficulty getting the gang to 1970, for Kain it would have been easy a short jump in time, but the energy needed for a long jump thousands of years probably would have severely drained him.

Although the whole theory of what kain is and where Kagato got his power might have been in a place where the realities and dimensions might have converged or been slightly exposed to Tenchi Universe’s Universe. It would explain why Kain is abnormally high powered and how Kagato boosted his own Juraian power, they were in a place where different energies and environments came together to change them.