I remember a flashback where Hildegard told Philia that Philia looked a lot like Hildegard when she was younger. I remember thinking it was odd, but damn for what I thought was a throwaway line to come back and this was the piece of the puzzle I did not know I was missing. It completely changes how I look at the story now.
It's completely unrelated but whenever they mention her being chased out of her home at 5yo I remember Shiki from Tsukihime, also with her being brought back many years later, also I see some resemblance between Akiha and Mia in that they were the only ones wishing for their return.
The main difference tho is that Shiki only got back cause of Akiha's selfishness (I've only read the remake), after her father's death she literally chased away every single family member against Shiki's return and abused her authority to silence any opposition. Also Shiki was 9yo when he was chased and the reason is... a bit more understandable.
Another difference is that Shiki
ain't even part of the family, he was adopted so he never actually belonged to the Tohno Mansion