
It says that Asisi's mother was Emperor Ivan's mistress (Caitel's father). Of course she could have had Asisi prior to becoming his mistress. Idk. http://www.mangago.zone/read-manga/daughter_of_the_emperor/uu/to_chapter-156/pg-24/

Yes she was the mistress, but in this chapter http://www.mangago.zone/read-manga/daughter_of_the_emperor/uu/to_chapter-112/pg-1/ during Asisi's point of view his father was shown. So they don't have any blood relation, they could be called step brothers in today's time but still no blood connection.
So Asisi is Caitel's half brother? Making him Ria's uncle? Or...(I don't feel like going back to see who's older) was Asisi born to another father? Making him a step brother?