Replying...
Intro. Daki and Gyutaro promised each other that they would always stay together, no matter what. This promise was made when they were humans, during their impoverished and harsh lives in the entertainment district. The promise was a cornerstone of their existence and bond: As humans: Gyutaro, despite his own suffering and abusive upbringing, worked hard to protect his younger sister, Ume (Daki's human name), and made a vow to never leave her alone. As demons: Even after centuries as demons, this deep attachment remained.

[Daki]

@Cyrus☆