While the theory that the gods in Dark Souls are largely based off of Japanese mythology sounds interesting and could very well be right, I should point out that they have a lot of similarities to the Greek gods too, and Dark Souls primarily being a jrpg with mostly western themes, it's probably intentional that they represent two pantheons from both sides of the globe.

As to the theory itself, well... It's a nice story.

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For starters, it doesn't say Seathe feared death itself. He pursued immortality, but that doesn't mean he was necessarily afraid to die. His main goal was to gain the Scales of Immortality, these scales are implied to be what made the original dragons what they were. There's also little evidence that Ornstein interacted with Seathe, and I doubt that alone even Ornstein could take him.

There's also little evidence that suggests Seathe knew Gwynevere, much less gave a damn about her or wanted to pork her.

Finally, the reason lightning type stuff is so harmful to dragons (not just Seathe) is because they were meant to hurt them, especially Sunlight Spear and Lightning Spear, the former being used by Gwyn to destroy the dragons' scales.

Much of this seems like pure speculation or literally made up, I'm not having a go at you man, but when you try to say that Ornstein "regained his full size" from Smough, which was supposedly stolen from him when there's nothing that confirms it, it sounds kind of... well, silly along with some of the other statements you made.

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Ornstein might have been the captain of the four knights because he was the captain of the four knights, he doesn't need to have been a prince or Gwyn's son to do that. Plus, you don't need to be descended from the Lords to have a powerful or special soul, anyone strong enough can build a very powerful soul it seems, the Lords and their kin just had theirs pre made.

His title was clearly just captain of the four knights, implying that for the most part his jurisdiction was over Artorias, Ciaran, Gough and later Smough, he was a body guard and special agent, not a general. Besides, why would Seathe give a damn about Ornstein or vice versa? Their interests had little to nothing to do with each other.

Question is tho, did From exclude just the firstborn from the game, or did they exclude him and his "image" aswell? Now I know there are missing statues of the firstborn, but who is to say that he didn't don the silver knight armour and acted as second-in-command to his father? In the second game, in HToF, the Old Dragonslayer is possibly just that, a Dragonslayer. It does not confirm that it is Ornstein himself. His Soul's description says that "The Old Dragonslayer is reminiscent of a certain knight that appears in old legends." Which suggests to me that there may have been more knights that wore Ornstein's armour.

Now an off little thought I just had. Flow of time is distorted, so what if Ornstein or the Firstborn tried to defeat the Abyss instead of/after Artorias?

What I sometimes think, is that the Firstborn MIGHT be the Old Dragonslayer. He was either tainted by, or enbraced dark majik, but despite being banished, he founded/obeyed the Blue Sentinels, because they had a good cause similar the one his little brother Gwyndolin had. Though that wouldn't explain the eagle-headed statues.

Perhaps HToF might even be of the Firstborns making. He ditched his God of War title and adopted his God of Sun title, and so people pictured him as the Sun God Ra.

Guys; it's Kalameet.

Personally I think thath Solaire is propably descended from Gwyn's firstborn... It would explain why hes so drawn to the Sun, since hes descended from the Lord of Sunlight, and why hes such a great warrior since the firstborn was a god of war. He propably doesnt have any idea he is descended from him, and his only goal is some force pushing him to try to find the sun that his ancestor lost...

Guys, what if, omg, Solaire's story actually really resembles Griffith's, albeit Soly's isn't anywhere near as dark. Can't believe I never noticed xD

Also, ummm, uhhh, Ra is the firstborn. .___.

Looks like DS3 put this rumour to bed.

DS3 finally resolves this age old question :D and the answer could not be more badass!

Could not belive he was Gwyns firstborn but it all makes sense now.

SPOILER ALERT!!

It's the Nameless King. His weapon description states that he was the heir of sunlight. Gwyn's Firstborn Son has his name unknown, which is why he is Nameless. He was stripped of his deific status because he was allied to the ancient dragons. Also, the description on his soul states that he was once a god of war, something that Gwyn's Firstborn was. There is no denying this. He was the head of the warriors of sunlight and Solaire was probably one of his most loyal knights.

It's kind of sad that they actually went and closed a plot point like this... But still, why was solaire at the kiln? I suppose it's because he actually was the chosen undead in his world. Or maybe he failed to kill Gwyn, just as Tarkus failed to reach OnS. If you think about it, Tarkus left his summon sign at the iron golem before dying, and it still persists, even though he is confirmed dead. So maybe Solaire died in his fight with Gwyn?