For centuries before the Seitei War the Soga are the most influential sorcerer clan in Japan because a woman in each generation can see. They advise on national threats. That is an office, not a personality. Chiaki inherits it from a main-line prophetess who died without children. The princess page is her title as hostage tag. This page is the institution Reddit kept calling “the Soga CIA.”
Advice, then cargo
Prophecy made them aristocracy and made them useful. Giyu can treat the office as something you hand to Mikaboshi. Kunishige’s later household, a bowl instead of a forecast, is a refusal of this room. We do not invent unseen prophecies. See Princess Soga, Izanami, Chiaki.