@PaChi To answer your earlier question regarding Arisen's hax/resistance from a long while back (Warning: Wall of Text incoming)-
Even within the gameplay alone, attaining resistance/nigh-immunity/immunity outright to Mind, Soul, Time, Curse, Poison, and Sleep Manipulation, as well as Petrification/Transmutation, Stat Reductions, and other such ailments (at least as far as it extends to beings of a similar power level/tier) isn't especially difficult. It's also worth noting that the Instant-Death roar of a dragon doesn't work on him, either, and that even without any resistance Dragons far stronger than him cannot under any circumstances inflict Possession.
Towards the end of the game? The Seneschal explains that Will is what turns the Eternal Cycle that the Verse's cosmology revolves around, that each Seneschal sustains their reality with their Will in order to maintain the laws of life, death, and volition that form the main conceptual base for the Eternal Cycle (relevant quotes ahead)-
"Will is that which led you to this place, and that which turns the eternal wheel of the world."
"Aye, there is life in the world, and with it death. Naught lasts forever. Each rises and falls in its time. But such is a death akin to that of pawns. They appear in this world, then vanish only to appear again, like bubbles in a mountain spring. As so it is with all that lives within this eternal world."
"Without volition, there is no true life. The world falls stagnant, dead as an ocean with no current to guide it. That volition is tempered by the struggle for survival. The decision, just like yours, to fight."
Etc, etc. Following this, you receive the quest The Great Hereafter:
"You have become the new Seneschal, keeper of the world. The Seneschal's Chamber shall be your home for eternity. It is the fate of the Arisen to dwell within these Chambers forever and always."
..."You are now Seneschal of the world. Find your own way to end the endless cycle."
Which you complete upon dealing yourself a "killing" blow with the Godsbane blade, signifying that the Eternal Cycle- that thing upon which the fundamental fabric of reality rests- no longer exists, and with it the multiverse. In spite of this, when the Arisen's Pawn falls to the "end" of the endless Everfall, and arrives once again in Gransys, the world functions entirely normally in spite of the Eternal Cycle's dissolution- a direct result of the Protagonist willing the metaphysical laws of reality to change while non-existant.
The very TL, DR of this all is Resistance (possibly Immunity) to Life, Death, Willpower, and Law Manipulation, as well as Manipulation of the aforementioned himself. Technically he doesnt "return" from non-existence, but it's questionable whether or not it can be said that he "exists" at all, at this point, and can interact with reality regardless. So...
So, if Lucemon were to absorb The Arisen into the Dark Area, to delete him from the existence and make him an aspect of the Seven Demon Lords? That's about the worst feasible thing he could do. At that point, not only would The Arisen cease to care about not existing, he would have direct access to the metaphysics of the Dark Area, and be able to reinstate the Eternal Cycle across Lucemon's existence (at least, if he is the Dark Area as you claim.)
What this would mean is that Nothingness would be replaced with Will/Volition, and require Will and Volition constantly in order to not sputter and die. (It may or may not also cease to be a BFR prison for everybody else absorbed.) Lucemon absorbing The Arisen would screw him over entirely, unless he has good enough immunity versus Death/Law Manipulation to suppress an effect able to effect an infinite number of infinite (in mass) universes with their own infinite timelines...
What one would probably need to deal with The Arisen at this point, other than just being a higher tier, is A: some kind of extra-powerful Sealing that finagles its way around all of this, B: the ability to block the above metaphysics shenanigans, and/or C: Power Nullification fit to take on a being of this magnitude.
Hilariously, Metatron is about the perfect counter for all of this, since as far as I can tell he no-sells Will Manipulation by virtue of being an aspect of YHVH's will rather than exhibiting Will of his own, and also nulls/heavily resists all of The Arisen's Light/Dark-element techniques (the best ones) in most of his incarnations. It probably isn't getting through to Yggdrasil, for similar reasons.
So, yeah, I still don't think he wins, but the initial wipe is just going to get Lucemon killed (or rather, incapacitated by virtue of being deprived of the Will he would then need in order to possess volition) if that's what's in-character for him to do.
So... yeah, that's my argument I guess.
P.S.: Can somebody, at some point please streamline Lucemon's Powers and Abilities section on his page? It's like, nearly two full pages long on its own, some of those elaborations can go in the Feats section.