Ilulu

Ilulu (イルル, Iruru) is a female dragon who belongs to the Dragons' Chaos Faction. Originally, she came to Kobayashi's world to destroy Tohru and then tries to drive Kobayashi away from Tohru. After a change of heart, she begins to live with Kobayashi as her third dragon resident.

Appearance
Ilulu appears in her human form as a woman of small stature wearing a black cloak with fur. She has a generous bust and even in her human form, she has dragon-like arms. Like Lucoa and Tohru, her horns are visible in human form.

Personality
When she first appeared, Ilulu was a psychotic, war-mongering force with a firm hatred for humanity. She initially was disgusted by the idea that Tohru could coexist with a lowly human, which led her to believe that Kobayashi must've been smitten by her. Her opinion on humanity was so strong, that she was shocked that Kobayashi would risk her life to save her so much so, that she was convinced that she was a trickster.

Once she redeems herself, Ilulu had some difficulties adjusting to human society, despite being roughly the same age as Tohru. As such, Kobayashi often tasks Tohru with babysitting Ilulu. She also was determined to find her purpose in life, even though her initial conclusion was too lewd to put into serious consideration. Despite being thousands of years old, she behaves like a child similarly to Kanna, even though there are a few obvious differences.

Background
When she was young, she used to play with humans and was even on good terms with them. But after her parents were killed by humans during an attack, her fellow dragons convinced her that humans were no good. She became sad and stopped playing with them, but she still thinks that humans have done nothing wrong. At one point when her parents were still alive, a human child she was friends with, made a doll for her. She went back home and showed it to her parents, but her parents didn't like it and destroyed it which made her very upset.

Plot
Sometime later, Ilulu makes Tohru a target once she realizes that she was coexisting with Kobayashi. Ilulu arrives at the city with malicious intent and engages in a battle with Tohru. Whilst battling Ilulu, Tohru restrains herself from going all out, lest she would unintentionally destroy the city as well. Ilulu is defeated, and she escapes.

Ilulu reappears again, having spied on Kobayashi and the others for quite some time. When Kobayashi informs Kanna that she would be unable to attend the Parents' Day event at her school, Kanna leaves angrily. Ilulu confronts her and attempts to manipulate her into destroying Kobayashi's workplace, claiming that it was her fault that she wasn't able to make time for Kanna. However, Kanna refuses and leaves Ilulu to ponder why she wouldn't comply.

Once again, Ilulu makes a reappearance, this time to Kobayashi herself. To understand why Kobayashi would live together with dragons, Ilulu concludes that it must be lust. She attempts to seduce Kobayashi with her large breasts to no avail. Angry at being rejected, Ilulu uses the remnants of her powers to transform Kobayashi into a male to prove that she was right. As a result, Kobayashi begins to feel urges towards Tohru and the other well-endowed dragons.

Lastly, when Ilulu was by herself, she is attacked by a Harmony dragon named Clemene and is beaten to near death. Before the final blow could be struck, Kobayashi intervenes, placing herself in danger. Clemene attempts to murder the two; at the nick of time, Tohru arrives and soundly defeats Clemene. Ilulu is taken to Kobayashi's house to be treated for her injuries. Even though she still believed that Kobayashi was trying to trick her in some way, Ilulu slowly began to turn over a new leaf, and eventually learned to love humans again. She later permanently began living in the Kobayashi residence, though to Tohru's chagrin. When Tohru explains to her that she needs to contribute to stay with them, Ilulu decides that she would marry Kobayashi and breed offspring with her. Naturally, Tohru takes offense by that.

Ilulu eventually gets a job at a candy store. Here she meets Taketo her boss's grandson who she falls in love with but she still loves Kobayashi more. He usually gets embarrassed around her. When Taketo's friends see him with Ilulu off duty they ask him if Ilulu and he were going out, he gets embarrassed instantly and stutters no. His friends eventually walk away and Ilulu says that they were going out to do something and he says that's not what they meant.

Taketo Aida
She first meets Taketo after she decides to work part-time and is hired by his Grandma. While Taketo was originally suspicious of her, the two eventually grew close that she ranks him after Kobayashi. She affectionally calls him Take and is willing to take a bath with him. She also enjoys teasing him with her body. In chapter 81, it is hinted that Illulu has now romantic attachment towards him as she points it feels different from when she was in heat.

Kobayashi
She tried driving her away from Tohru. However, after being saved by Kobayashi and living with her, she's now deeply attached to her and wants to breed with her. Kobayashi also cares for Ilulu and treats her similarly to how she treats Kanna but is shown to get easily frustrated at her large breasts.

Tohru
She tried to destroy Tohru but failed, due to her overwhelming power compared to hers. Even after Ilulu redeems herself the two were still cautious of each other but were able to put aside their differences for Kobayashi's sake. Like Kanna, Tohru teaches Ilulu how to live with humans.

Trivia

 * Like how Kanna recharges with electricity, Ilulu eats fire.
 * She explains that her breasts are big because they are her flame bags and store a lot of fire in them.
 * She's currently the only dragon of the main cast who's dragon form hasn't been revealed.