Eyes of Nidhogg
The Eyes of Nidhogg were an immensely powerful relic that contained the power of one of the strongest Dragons to ever live. For over 1200 years, the eyes were held by the Ishgardian Orthodox Church, one buried with the son of the first King Thordan and the other given to the Azure Dragoon. Their power was used to increase the strength of any who held them well beyond the limits of a mortal man.
History
In the beginning of the Sixth Astral Era, Dragons and Elezen lived in peace together after a long war over ownership of the land of Abalathia. Though most Dragons accepted the Elezen and vice versa, there were some who held the other in distrust. Nidhogg was one such Dragon, refusing to fully trust the Elezen King Thordan but not willing to shatter the peace they currently had. This peace would be broken regardless when the Ascians informed King Thordan of the source of the Dragons power: their eyes. A few of the Elezen, the king included, began to covet the power of the Dragons, and desired it for themselves. Thus, they laid a trap.
Sending a message to the Dragons stating they wished to speak, they cornered and murdered Ratatoskr, the sister to Nidhogg, and consumed her eyes. Learning of this, Nidhogg was overcome with despair and rage. He immediately made for the king and his knights twelve with intent to kill. Unfortunately, having already imbibed the power of Dragons, the king and his men were well beyond the limits of normal men. A brutal battle ensued, and though King Thordan and four of his knights were killed, Haldrath, the king's son, managed to best the Dragon and pull his eyes from his head. While not lethal, the damage sustained caused Nidhogg to flee. seeking counsel from his brother Hraesvelgr, Nidhogg convinced him to turn over one of his eyes so he may continue his quest for vengeance.
The Eyes of Nidhogg proved to be extremely powerful, and were kept as relics instead of being consumed. The people of Ishgard would use the power of the Eyes against the Dragons in the Dragonsong War. The Eyes could be used to track Nidhogg, however the reverse was also true. Due to being connected to Nidhogg, wielding both Eyes at once would greatly affect the wielder. After the Eyes destroyed Haldrath, it was decided that no one could wield the power of both eyes without being corrupted by Nidhogg's malice. Therefore, they buried one of the eyes with the son of the king, and gave the other to a Dragoon of Ishgard who proved to be the strongest, and bequeathed to them the title Azure Dragoon.
For centuries the Eye would be passed from one Azure Dragoon to another, until it came to the hands of Estinien Wyrmblood, an Elezen with a particular hatred for Nidhogg. As a boy, Estinien watched as Nidhogg razed his village to the ground. He only survived thanks to the previous Azure Dragoon Alberic.
When the Warrior of Light joined the fray and plans to end the Dragonsong War without further casualties failed, Estinien led them to Nidhogg's lair to confront the Dragon. Using the power of the Eye, Estinien dealt the final blow, pulling Hraesvelgr's eye from his head. Realizing that the Eye they had taken was in fact not [[Nidhogg]'s, accompanied by a vision via the Echo revealing that Haldrath had taken both Eyes, the Warrior of Light and Estinien made to confront Archbishop Thordan about the truth of the cause of the Dragonsong War.
Eventually, the Warrior of Light caught up to Archbishop Thordan and learned of his consortment with the Ascians. Using the power of The Eye of Nidhogg, the Warrior of Light slayed Igeyorhm. Archbishop Thordan appeared then, wielding the other Eye of Nidhogg and used its power to summon King Thordan as a Primal, using his body as a catalyst. With the Eye set in his blade Ascalon, King Thordan challenged the Warrior of Light, but fell to them in the end.
When Estinien arrived, he attempted to hold both Eyes, but the malice of Nidhogg overwhelmed him, turning him into Nidhogg's thrall. Reborn, Nidhogg proclaimed that he would bring the end of the Dragonsong War with the death of all Ishgardians.
At the final battle of the Dragonsong War, the Warrior of Light managed to defeat Nidhogg and wrest the eyes from Estinien's body. Deeming them too dangerous, Alphinaud and the Warrior of Light cast them over the Steps of Faith and into the Aetherial Sea below.
The Eyes would not stay there for long, however, as Elidibus would collect them and give them to Ilberd Feare to enact his revenge upon the Garleans by summoning a massive Primal likened to the Elder Wyrm Bahamut: Shinryu. Matching the rage of the Eyes with his own, The Griffin gave his life to make his wish come true, and Shinryu was summoned.
Though it disappeared shortly after being confronted by Omega, it was later hunted and captured by Zenos yae Galvus, who used the Primal and the power of the Eyes of Nidhogg, as well as his newly obtained powers as a Resonant to merge with the Primal in order to defeat the Warrior of Light. In the end, the Warrior of Light emerged victorious, and Shinryu and Zenos yae Galvus were defeated, leaving the Eyes finally drained of power. Not one to take a chance, Estinien destroyed what remained of the Eyes, ensuring their power could never be used again.