Fafnir

This is gamer guy shy dragon dude
In his human form, he appears as a long, straight haired man in butler attire with a mail coach cravat tie. He has red eyes which can change color and size depending on his rage. He has a calm, collected demeanor which reflects his slightly gloomy face.

When he is in dragon form he appears as a towering dark dragon with 3-4 pairs of pure red eyes.

Personality
In the beginning of the series, Fafnir abhorred humans for everything they were. As the series goes by his heart warms up to a human with similar interests and takes on a sensei-student style friendship with Makoto Takiya. His hatred for humans turns into more of an indifference to them, and more of a pain to get to know them rather than just kill/ignore them. He appears to dislike spicy food, as when Takiya made some curry, he asked if it was "mild" and refused to eat Tohru´s soup after learning that it was spicy.

Due to this, he became extremely addicted to video games and other Otaku interests since his life style of a cursed dragon can easily accommodate it. He is hardworking and diligent for his passions as seen with his multiple all-nighters to play games.

Powers
Fafnir has the ability to create very potent curses. The incantations for the curses he writes are so powerful that even a human without magic can curse someone with it.

Like all dragons, Fafnir's physical strength far exceeds that of a normal human. However it would also appear his strength exceeds Tohru's as he was able to effortlessly catch a ball she threw, then send her flying back upon throwing the ball back to her.

Relationships
Makoto Takiya - His roommate and friend, Takiya is the human who introduced Fafnir to video games. Both Kobayashi and Tohru were surprised when he accepted Fafnir as a roommate without question or worries. The two eventually bonded close enough to the point where Fafnir who have been infamous of being solitary in his past accepted a nickname that Takiya made just for him, stating that he "doesn't mind it". Fafnir eventually got comfortable enough with the Otaku lifestyle that he tags along with him to conventions and helps him set up, later on setting up his own stand (with no sale-success).

Tohru - Tohru seems to be his friend and possibly a student. She often calls him early in the story to ask for his advice. The two seem to share mutual respect and care for one another's well-being to an extent; helping out each other at a moment's notice to their best knowledge.

Kobayashi - Not much interaction is shown between the two but despite Fafnir's hostile first impression on her, Kobayashi seemingly went along with it and the two seem to respect one another's boundaries. He doesn't seem offended by Kobayashi's outright rejection of Tohru suggesting him to stay in the Kobayashi residence but neither does he seem to hold the place in any specific significance compared to the rest of the dragon cast. Nevertheless, both Kobayashi and Fafnir doesn't seem to mind one another's company.

Quetzalcoatl - Little is known of the two's relationship if at all, but the two doesn't seem to mind each other's company. Both of them however, share a similar trait in that Tohru regards them both as her seniors/ teachers, often asking for their advice. Comically albeit logically, Tohru's 1st choice for advice is always that of Fafnir but brushes it aside for Lucoa's instead.

Elma - Both Fafnir and Elma enjoys a level of grandeur evident in their joint play for elderly.

Kanna - Unlike Tohru, Fafnir doesn't show any particular bond with Kanna nor does he hate her companionship. The two often interacts on a similar way to that between Tohru and himself but at a distance in comparison.

Trivia

 * He bears a resemblance to Sebastian Michaelis from Black Butler, due to his appearance and even his Japanese voice actor.
 * Tohru calls him Mr. Fafnir.
 * Fafnir is also the name of a dragon in Norse mythology, who is the son of the dwarf king Hreidmar.
 * He created a circle for Comiket and sold a volume on curses - he was unable to sell a single copy.
 * His true/dragon form is 20 Meters Tall.