Who dis really?
Hypothetically IF it is our tuxedo penguin-looking demon... that'd be insane foreshadowing from Toboso.
Sebastian Michaelis -> A major interpretation is the biblical symbolism Michael evokes the Archangel Michael, a figure tied to divine judgment and protection, so giving a demon that name feels like classic ironic symbolism from Yana... especially since Sebastian is anything but holy. (Most fans already know this.)
This panel captures the irony perfectly: a demon illuminated like a saint while carrying out murder in a sacred place.













