Just thought what would happen if Pantalone / Tianyu actually lost his Dottore too, what would he do afterwards.... ( I'll explain below the original headcanons so it makes sense how baizhu and panta are twins ^^ )
Both were born about 400 yrs ago. As Tianyu detested the kindness of his brother that was shown to strangers after they struggled both too much, he left that one night. After waiting for his return, Baizhu had assumed his brother had died, just as their parents had died from an illness none could cure.
On the night Tianyu left, he was attacked and killed by a vampire, then turned, too. He became extremely weak without blood, as vampirism acts like an illness. The one time he managed to return, and they were both still teenagers, Baizhu had been granted a vision for his kindness and openness to others, and his determination to help people afterwards. After Tianyu had witnessed his brother being blessed from afar, he still Refused to return and chose to diverge entirely, swearing revenge.
The events that occur afterwards are similar to canon, except Tianyu was passed around from doctor to doctor until reaching Dottore's lab at around 20 years old. At that time, Dottore similarly takes Interest in Tianyu mostly for the vampirism and chooses instead to see what he can do to improve such a new condition.
As their relationship developed, Tianyu brings up his brother dilemma to him and they both discuss it over time.
Dottore suggests experimenting on freezing Soul and body in time, which would later on help with the creation of his segments.
Baizhu was then captured by the Fatui at the request of Dottore, while at the same time, Tianyu climbed in ranks to become the 9th Harbinger. The experiment was successful, And Baizhu was thus frozen in time, asleep, for an extended duration of time.
Pantalone's goal was to awaken his brother in a time and place he wouldn't recognize, first to make him feel exactly how he felt when he woke up as a vampire, and two, so he would still be alive To witness the world change exactly how he wishes for it to be.
Baizhu would then awaken confused with no recollection of the past, continuing his life still at the age he was frozen into. After that, his life continued much like canon, meeting Changsheng and all.
The biggest trouble he has currently is to figure why he cannot remember what happened, how come time doesn't match, and what happened to his brother for him to change so much.