The Incubus King

Though the ostensible main villain, the Incubus King seems likely to play a smaller role in the plot. Though he holds one of the biggest Soul Shards, he's not necessarily the most powerful person with one. He's definitely not one of the most competent, since he's dangerously stupid and ruled by impulse.

Story
His arrival on Arclent (from Renthnor) completely changed the continent, setting off the war and destroying multiple nations. Since then, he's grown complacent and mostly sits in his lava castle. It seems like he leaves most of the management of his empire to Iris and inspires very little loyalty in anyone not in his direct presence.

So far he's displayed several fetishes that are on the odd side, even for succubi. These include the "crownjob" and something that involved a giant chess set made of feces.

He is incredibly selfish in all that he does, taking relentlessly from those around him. During the Third Arclent War this culminates when he reveals his "secret weapon," succubi that he has fucked until he was able to rip away the sexual parts of their soul, resulting in the Unsuccubi. This was previously thought to be impossible, but it is noted that it would be possible if an Incubus King was purely selfish they would be able to do it.

He insists that he is the only one and demands everyone call him Incubus King. During the first meeting of the Gathering he proclaims himself to be the:

The real powers have their own titles and don't mind that much indulging him, to a point of course, but some of the lesser ones are pissed about it.

During the Gathering, Yarra experiences the full scope of his power and only the timely intervention of both Esthera and Estaven allows her to leave the reunion as a free succubus and not as some kind of sexy zombie.

But in one sense he is exceptional, because he has two amazing subordinates that helped him: Iris - not dedicated to him personally, but to the people of his domains - and Riala - a mage of great power and knowledge, used as his personal errand girl for humiliating tasks. Of course, he doesn't appreciate them any more that he does his kitchen's servants. Riala has betrayed him already by giving Simon his soul shard, while Iris is likely to betray him as soon as she believes it's in her people's best interest to do so. Riala has already been caught and punished in some way that seems to have broken her will, so she may actually be more of an asset than ever. During the Third Arclent War his rampant mistreatment of all those under his rule has come back to bite him, as both Riala and Iris have turned against him. Even more of his forces would turn against him when he reveals his unsuccubi, succubi that have been sexually toremented to the point that all sense of sexual desire has been ripped from them turning them into rampaging beasts with no desire other than to die.

It would later be implied that near the end of the war in a conversation with Simon, that for all his bluster, the Incubus Emperor was actually well astute and aware of how others perceived him, but the power of his shard made it so that his word was final. It is also implied in the final battle that the Incubus Emperor was actually very insecure about himself and that the shard didn't change his personality nor was he truly the way he acted trough out the first three chapters of the game. As part of his inferiority complex he hated being reminded that he was chased out of Rethnor and that anyone who challenges him. He is also troubled by Simon's more serious nature, claiming that the power they have could make them do whatever they want, also implied that he may have been an adolescent when he received his own shard.

Wiki trivia
As coined by Argenten we've begun referring to him on the wiki and forums as: "Arsehole of Arclent" to help distinguish him from all the other Incubus Kings. (Because it fits him pretty well and cuts the confusion about what we're talking about down quite a bit.)