ONA
Description
Fafner di Nidhogg is one of the seven new God Warriors of Asgard, serving under the priest Andreas in the anime Saint Seiya: Soul of Gold. Born and trained in Asgard, he is a warrior of Odin who guards the chamber of knowledge known as Svartalfheim within the great tree Yggdrasill.

Physically, Fafner is depicted as a tall, thin man with long grey or silver hair and a pale complexion. He often carries a sinister smile, and his posture tends to loom over others, giving him an unsettling presence. He is officially described as the most malefic and cruel among the seven new God Warriors. Fafner possesses an immoral and inhuman personality, showing no concern for innocent lives; he coldly views the citizens of Asgard as nothing more than test subjects to be used and discarded as tools. His arrogance is matched only by his cowardice, as he prefers to rely on traps and stratagems rather than engaging in direct combat, and he will attempt to flee from a fight when at a disadvantage. He is a firm believer that the ends justify the means, rationalizing his cruel experiments as necessary for the prosperity of Asgard.

As a scientist serving Andreas, Fafner is the mastermind behind the horrific human experiments conducted within Yggdrasill. He is the creator of the new Odin Sapphires, which are used to augment the power of the God Warriors and, ultimately, to control their minds. His primary motivation is to complete his research and serve Andreas's grand plan, which involves manipulating the divine tree. He operates by preying on the innocent and ill, offering free health treatments as a guise to select suitable subjects for his experiments to further the growth of Yggdrasill.

Fafner's role in the story is that of a primary antagonist who directly confronts several Gold Saints. His initial experiments are halted by Aries Mu, who investigates the disappearance of villagers. Later, he captures a young Asgardian girl named Helena, who becomes a friend to Pisces Aphrodite and Cancer Deathmask, using her to create a new sapphire; this experiment ultimately leads to Helena's death. He further escalates his cruelty by capturing Helena's younger siblings to use as hostages and for further experimentation.

His key relationships are defined by his antagonism toward the Gold Saints. He battles Aries Mu on multiple occasions, initially overpowering him with the aid of Yggdrasill's power. He also confronts Pisces Aphrodite when the Gold Saint attacks his laboratory to rescue Helena. Finally, his most decisive relationship is with Cancer Deathmask, who seeks revenge not only for Helena’s death but also for the enslavement of her siblings. Deathmask ultimately becomes Fafner's captor.

Throughout Soul of Gold, Fafner does not undergo a heroic or redeeming development. Instead, his desperation and cowardice become more apparent as the Gold Saints grow stronger. In his final battle against Aries Mu and Cancer Deathmask, Deathmask transports Fafner to Yomotsu Hirasaka, the entrance to the Underworld. Even in defeat, Fafner tries to use his hostages as leverage, threatening that the children will die if he perishes. In a final act of poetic justice, Deathmask, empowered by his God Cloth, uses a technique to bury Fafner face-down in the ground of Yomotsu Hirasaka. There, he is condemned to be eternally trampled by the souls of the dead, suffering an endless torment that matches the cruelty he inflicted on the living.

In terms of abilities, Fafner wields a God Robe named after Nidhogg, the dragon that gnaws at the roots of Yggdrasill in Norse mythology. His primary weapon is a whip-sword called Ridill, which is part of his God Robe. He also uses a double-headed spear in battle. His signature attack is the Dragonewt Bullet, where he concentrates his cosmos into Ridill to fire powerful blasts or spiritual bullets at his opponent. Thanks to the power of Yggdrasill and the land of Asgard, his God Robe provides him with strength and speed comparable to, or even surpassing, that of a Gold Saint, allowing him to break through defensive techniques like Aries Mu's Crystal Wall. However, despite these formidable powers, his reliance on underhanded tactics and his cowardly nature ultimately lead to his downfall. His name is a direct reference to two dragons from Norse mythology: Fafnir, the greedy dragon slain by the hero Sigurd, and Nidhogg, the serpent-dragon that chews on Yggdrasill's roots. This duality fittingly reflects his role as both a greedy, cruel scientist and his close association with the great tree Yggdrasill.