(seriously, why the hell is the name of the Wendish Empire not dependent on culture...)
The rule of Butavas III began with a war to put his aunt on the Byzantine throne. The superior Lithuanian armies were more than enough to beat the Byzantines, who had to deal with not just the Lithuanians, but other Greeks as well, as the Abkhazian duke was pressing a claim of yet another woman for the throne. The war was soon won, but the duke of Abkhazia dud not give up. to the contrary, once it became clear the new empress was not only a foreigner but also a heathen, and was not planning to convert to orthodoxy any time soon, all of the old loyalists joined the rebellious duke. That was no hyperbole. ALL vassals joined, with the exceptions of children and barons.
The Lithuanian armies were again too strong and thousands of Greek soldiers fell to the Lithuanian heavy infantry. When Butavas III saw that an army larger than his own was sieging Constantinople he almost despaired, but luckily the Abkhazian duke heard of the slaughter of his allies in Greece, and without realizing he still had a reasonable chance for victory he surrendered.
All but four vassals (ignoring barons, bishops, and mayors) were imprisoned and the new pagan empress slowly began demanding the prisoners to convert to the Romuva faith, revoking the titles of those who refused.
Mean while, Emperor Butavas III was trying to kill his brother, who was king of Lithuania, Pommerania, and Bohemia, but after years of trying, he just did not manage to do it.
In the end he decided to imprison him with some weak excuse. The king's fellow vassals did not care. much of the treasury Butavas III inherited from his father was spent on bribes so the usually rebellious empire was, internally, at peace.
Stranger things happened in Persia, however. A second Gnostic liberator had appeared, and this time the Muslims did not manage to subvert to Persians again.
Butavas III hated his eldest kid. Fuck you Butters.
(At first I thought this was a bug, having a vassal of the same culture, same religion, same dynasty, and 100 religion starting an independence faction... Sending a spymaster to scheme in their capital stops shenanigans like this though.)