Not much is known about Fafnir except that he was previously killed by the original Siegfried who wielded the Demon Sword Gram but was later revived by the Norse Gods. However despite his perverseness, he is shown to be exceptionally faithful to those he serves, as he frequently lends his powers to Azazel, and protects Asia while risking his own life in the process, and didn't stand aside despite his grave injuries. According to Ddraig and Albion, Fafnir wasn't as perverted in the past as he is right now. In his first appearance, Fafnir is revealed to be a perverted Dragon with a fetish for panties, sniffing them and referring to them as "treasures". As mentioned by Sona, Fafnir has a tendency to collect treasures throughout the world. Little is known of Fafnir's personality due to him being sealed in Azazel's Artificial Sacred Gear, as well as the fact that there are very few instances of him being described. In Outrage mode, Fafnir is able to manifest a pair of wings.
In his first appearance, Fafnir had a pair of Asia's panties on his horn. Fafnir is a golden Western Dragon that is more than 10 meters tall, who lacks a pair of wings on his back, which are possessed by most Western Dragons, and has a horn on the tip of his nose.