so what heteromorphic being is Sebas?
The Dragonoid race is likely the one Sebas was part of as Shalltear refer to him as such during Overlord Light Novel Volume 3 - Chapter 1: Herd of Predators.
Here is the quote from Shalltear about Sebas:
“Sebas — could you say that again? Or are you saying that a Dragonoid like yourself, in that form, wants to —”
Sebas was dragonic race
would be cool to him in his dragonoid form
What do you think?