Much like tieflings, daevas are a material creature infused with the immortal essence of an astral being.
In Escarnum, daevas would not be understood as a “species”, but as a unique occurrence—most likely the result of a celestial being attempting to empower a loyal follower. It’s likely that such a creature might be unaware of its own nature, and perhaps even mistake itself for an Awakened if it seems human-like.
The memory of other lifetimes gives the daeva a unique rolepaying hook that you might find appealing. In Escarnum, this especially has echoes of the Felbraug shared mind; we encourage your GM to allow “re-skinning” the daeva as an unusual felbraug, if this is appealing to you. Alternatively, this could represent a mortal of any species who carries another intelligence with them; perhaps a curse, perhaps a bound celestial or an ancestor ghost, perhaps even a symbiote of the far realms.
A daeva might also be a celestial in material form. Devils and angels may oppose one another, but they are of the same essence. Both exist only on the astral plane, and both must use a willing mortal as a conduit if they wish to exist on the material.
In this situation, it’s important to remember that the angels of Escarnum are not especially kind creatures. Celestials usually bargain in good faith, but they are also dispassionate and utilitarian; the values inspired by their immortality and distant perspective are generally inscrutable to mortals. Even if they are working to good ends, they are still using mortals as a means to that end.
However, like devils, angels often find that staying material for an extended time allows mortal ideas to begin creeping in…