I communicated with the author and inquired them about a few points, according to them :
1- Asue's race's name [Asfel Raja] is coined.
2- Unlike other novels like (Dungeon ni deai, Arifureta, Goblin slayer....etc.) monsters in Re:Monster don't have any characteristic biologic factors, something like magic stones. In the first place, they don't attack others (be it humans, beastkin, demons, or other monsters) because they're monsters, rather THEY'RE CLASSIFIED AS MONSTERS BECAUSE THEY'RE ATTACKING OTHERS BELLIGERENTLY, MOST IMPORTANTLY OTHERS CAN'T NEGOTIATE WITH THEM, EITHER BECAUSE OF LANGUAGE BARRIERS, ARROGANCE, GREED...etc.
They don't have any defining biological features, they're monsters simply because that's how interacting civilisations (be it human, beastmen, demons or others) see them. In short, monsters are creatures harmful for civilization. And while Ogres are generally monsters, usually Ogre Mages are not because they're more open-minded and can negotiate and live multi-race societies, that's also what makes Lords non-monster unlike Ogres even though are very closely related.
3- Those with Noire soldier can strengthen their bodies by eating any creature, although it was stated in the novel that they can get stronger by eating monsters, that's not exactly true. It's just that even for Noire soldiers, eating creature not recognised as monsters is too brutal, but as long as it's not human they can practically get stronger by eating any creature, but of course the strengthening isn't endless. At some point you'll stop getting stronger from eating a creature, that also means Redhead at some point stopped eating from Rou because it already became useless. Although the stronger the creature you eat, the higher the strengthening rate, that doesn't mean that if Redhead were to eat parts of the White stag when she was really weak in vol.1 she'll suddenly jump dozens of levels by a single bite, to make it easier lets say that if she ate 1kg of kobold meat her physical strength will increase by 5 and if she ate 1Kg of ogre meat=20 and 1Kg of Fomor meat=50, even if she ate 1Kg of White stag meat she'll only get 50 units increase in physical strength, it's her body's limitation, while if she ate it at the time of the kingdom's noble faction's rebellion she may get as much as 500 units increase in physical strength. In short no matter how strong the creature you eat is, there is a limit to how much increase in power your current body can endure.
~Obarou