As a special family among humans, the Black Rose has a unique connection with the Abyssal Demons. The Demon kings of the Abyss, who are like the Grim Reaper in the eyes of ordinary people, can also get along well with them, except for the Higanbana...
In fact,
Sebastian had never had direct contact with Higanbana.
After all, when Sebastian came to the Winter Forest, Higanbana had already run away from home and betrayed Yumo. His understanding of Higanbana, or rather the understanding of the members of the Black Rose now, all comes from Yumo's other children and their elders.
That Abyssal Demon is even more ancient and powerful than the Sword Demon Pierre.