For those wondering why Kaede (the Tengu woman) never went back to Hakurou:
She's a semi-spiritual lifeform and didn't use to have a lifespan. On the other hand, Ogres (including those who are human-ogre mixed blood like him) have a lifespan the same as that of humans.
The manga adaptation here skipped it, but in the novel we get to know that Kaede actually thought that Hakurou had long died of old age.
And yet, Hakurou has been around for close to 350 years now.
No one, including in-story characters, knows the reason why he was able to live so long for sure.
The best theory is that he got a sort of longevity trait from his human otherworlder grandfather(Araki Byakuya), and that this trait simply didn't appear/activate within his grandfather nor in Araki's half-human half-ogre daughter (Hakurou's mother).
So in the end, Kaede had no way of knowing that Hakurou was even alive. She thought he had died centuries ago.
Heck, when she noticed her pregnancy, it was already at a time when she thought that Hakurou had already died of old age.