Fafnir

Fafnir (ファフニール Fafunīru) or Takeshi Ooyama (大山 猛 Ōyama Takeshi) is a supporting character in the series. He is Makoto Takiya’s roommate and friend.

Appearance
In his human form, Fafnir appears as a young man in butler attire with a mail coach cravat tie. He has long, straight black hair in a loose ponytail with bangs covering his right eye with small glasses on the bridge of his nose & red eyes which can change color and size depending when enraged. He has a calm, collected demeanor which reflects his slightly gloomy face.

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

He is also able to transform into a monstrous humanoid form with purple skin, a bulky upper body, a mouth with several rows of big and sharp fangs as teeth and two horns.

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 or 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.

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 (dragons don't actually need to sleep to stay healthy and active).

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.

Makoto Takiya
Takiya is Fafnir's human roommate/friend and the person 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 (without being to sell even a singlecopy of his works, though).

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 or 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 more sane and practical suggestions instead, as his advice is always "kill them", be it about guard duty or laundry.

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

 * Fafnir bears a resemblance to Sebastian Michaelis from Black Butler due to his appearance and even having the same Japanese voice actor.
 * Fafnir also has an strong resemblance to Alucard from the Castlevania franchise in his 21 century alter-ego, Genya Arikado.
 * 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.
 * Fafnir created a circle for Comiket and sold a volume with actually effective and often lethal curses - he was unable to sell a single copy.
 * Fafnir true resp. dragon form is 20 Meters Tall.
 * Fafnir dragon form bears a striking resemblance to the Ogdru-Jahad from the Hellboy comics.