Invincibility field

The invincibility field is an aura given to Demon King Ssulal by Planner in order to make the demon king invincible to attacks by the protagonist race. This invincibility field was incorporated into the blood of the demon king, and since Dark Lords get their powers from the blood of the demon king, they also received invincibility fields (this was incorporated retroactively, so dark lords older than Ssulal, such as Kayblis also obtained an invincibility field). In game, this ability was first shown in Rance III when dark lord Satella deflected an attack by use of an invisible orb around her. This original orb concept of the invincibility field has changed a lot since Rance III and has since become a skin tight aura around the dark lords. As stated earlier, this aura around them make them invincible to all attacks caused by both past and present protagonist races (currently humans), but it does not make them immune to attacks from other sources like other dark lords, devils, angels and two of The Legendary Five, Chaos and Nikkou. These attacks will temporarily shatter the invincibility fields, making it possible for attacks from the protagonist race to damage the dark lords for a short while.

While humans cannot normally pass through the invincibility field, a few technologies have been created to attempt to do so with mixed results. The Toushin were powerful mages turned into machines by M.M Rune in order to fight the dark lords during demon king Gi's reign. These machines fought on par with the dark lords, but did not have the ability to pass through their invincibility fields, making them only able to fatigue the dark lords. A success story comes from a technology invented by a human named Pi-R. He managed to extract the source of the dark lord's power, the Demonic Blood Soul; though, instead of using this incredible technology to allow humans to battle dark lords on equal footing, he decided to take the demonic blood soul from a dark lord and consumed it; overcoming the will of the previous dark lord, Pi-R became a dark lord himself.

Another technology was created to defeat dark lords: the Red Eye. Before it could be tested on a dark lord, demon king Nighcisa caught wind of it, found it and gave it his blood, turning it into an insane dark lord. It is not certain if the Red Eye would have been able to break through the invincibility field before turning into a dark lord, but it should have been quite powerful, considering it is one of the few beings in history to have a level 3 magic skill.

The definition of "attack" used to define what the invincibility field will block or not does not seem to perfectly match today's current definition of attack. For example, it is possible to sexually assault a dark lord because the invincibility field does not consider sexual assault an attack; though this is normally a terrible idea because dark lords are generally extremely powerful entities with either extreme physical or magical prowess.