I have already given quite a few reasons why in my previous posts and to detail everything would require its own wiki. I am not going to do that.

Aside from him being able to wipe everything to perpetual nothingness (existence itself, not some mere universe)...

He is truly immortal so long as there is life and death which, in itself, defines existence. If he destroys everything and then creates everything again he will once again exist while at the same time being the only thing to exist even in nothingness... if you can even qualify zero point as being "nothing". Sorry, but Demonbane doesn't even wield a fraction of just that power alone... this is the difference between mortality and Necron.

Symbolism...
His appearance and reason for being there at the end of the story, Kuja's connection, the world's connection, desire for nothingness of the world... Kuja... mankind.., etc. He was not defeated but simply decides to observe human's will and power... when he vanishes the eyes closing and his speech as well as continual existence. Life and death itself.

There is quite a bit more but I'm not really going to put up with all that effort.

Burden on proof is on you... What leads you to believe that Demonbane can destroy something truly omni-potent or erase existence, itself? He can't. He is effectively the equivalent of max stats but those stats are not infinity.

So off topic... and we are the only ones even discussing in this thread now.

Spoiler's here, sorry but at this point it needs to be said. Necron is what happened when Kuja destroyed the Crystal, the beginning of everything. Weather or not Necron actually would have actually returned the world to the "Zero World, where there is no life, and no Crystal to give life" is kind of moot. With the Crystal gone, nothing should have ever existed. It is simply Zidane's and etc memories, and will to live that even allowed them to fight Necron. This concept has happened throughout different final fantasies.

Necron seems to be Kuja's will to destroy everything. Focused through the Omnipotent Crystal, it was given a life, and a purpose. Only when the party show's the will to live is stronger than Kuja's will to kill all, did Necron leave.

Essentially this makes Necron Omnipotent, incapable of being defeated except by an idea: he had to be convinced that he was wrong. That and Kuja also decided he was wrong, and was the reason they escaped Memoria in the first place, perhaps even the reason Necron gave up.

That is not evidence.

Second game. Summons every Demonbane that can, will, does, doesn't, may, may not, and will never exist.

Athleta Aethernum... or whatever... From the second game

It can summon literally infinite Demonbanes with that attack to Zerg the opponent.

Nice theory.

But I have hard evidence to disprove you.

Translation of page 301 of the 20th Anneversay Ultimanias.

You are giving baseless speculation.

While F8ted makes some decent points some of it I can agree with and some somewhat off... to go with Demonbane being able to defeant an omni-potent entity... by zerging it? I think you fail to understand what omni-potent means entirely. You can not zerg, or destroy such a thing... I'm not even sure if I should bother continuing to discuss this just because I have made this point repeatedly. No matter what... something that is omni-potent can never be destroyed, period.

EDIT: I should also mention that the Ultimanias are not canon. They can be used to find information and a lot of it is accurate but there are quite a few inaccuracies as well. Kuja's fear and desire to destroy everything along with the direction Terra and Gaia had pushed the events to bring about destruction. This summoned Necron who has been observing since the beginning and he decided he would return everything to nothingness. Zidane's group showed Necron the will of humanity and he decided to observe (eyes closing during end of battle CG as part of the symbolism, etc.). He lords over death and death rules over life. There is a ton more to this. It is quite deep, though not obvious which is why so many people don't understand Necron's sudden seemingly random appearance at the end. Quite an impressive feat on Square's end.

Gespens... are you really arguing that a sword is more powerful than a being? A sword can be AWESOME, but without someone to wield it effectively its just an idiot using a really good sword. Do you think that Bob the Guard would be scarier with Demonbane than Sephiroth would be with Masamune?

I think that the idea of a great weapon is awesome, but that has no bearing whatsoever on who is the most powerful CHARACTER to potentially transition from FF to LoL.

Life existed after the fight, this meant he Crystal was never destroyed. Kuja already showed that he could manipulate the crystal to do essentially what Demonbane's self-summoning is capable of doing. He could have, in fact, created himself again infinite number of times. The Crystal itself could create infinite Necrons. Kuja used the Crystal to summon Deathguise, and the Chaos's. It is more likely that Kuja in a way "Created" Necron when his hatred and will to not live overcame his will to defeat the team. He could have already lived for all existence at that point, because the Crystal was, as far as Gaia/Terra is concerned, the beginning of time.

It makes the Demonbane point moot. By the summon infinite=win logic. Kuja could just sommon his own army of Demonbanes, who in turn could summon their own arbitrarily large number of Demonbanes. Kuja, over any other character in the FF universe, even Ultimecia, was the most powerful. He controlled "God"

I would have to say Sephiroth(a little fan-crazed, but hear me out). He has a 7-foot long sword, which is enough to say he can be a ranged character. also, he put himself within the planets lifestream, ultimately giving him the strength of the planet, essentially causing his fighting abilities and magic to be increased significantly. third, he already had excellent fighting skills to begin with, able to take down hoards of enemies within mere moments. fourth, he can call meteor, which the planet itself had to stop with its entire might, which is saying something. and last, he has gone insane, and worldly power+insanity=crazy strong.

Let's make it more broken by doing adittionnal damage the more CS the targets have

Waka would be the perfect counter to Oriana.