Lamia

Lamia (or Lami-tan as Yuka nicknames her) is a small, childlike Demon who is the daughter of Laymia, Pillar Baron of Behemoth's 34 Pillar Division. She initially provides her services as a nurse (assistant doctor) when healing Tatsumi but has since become more of a supporting character in the series.

Later in the series, she seeks Takayuki's help to find Lord En on Hilda's request. Furuichi suspects her of being a tsundere. His sister Honoka in turn almost reports him to the police when she suspects him of being a pervert.

Appearance
Her age is unspecified, but her appearance is that of a pre-teen girl. Much like her mother, Lamia has pink hair and green eyes. She wears a white lab coat with a grey polo underneath it and red neck tie. She wears a blue short skirt with a pink trim that is far above her knees, this leads to numerous comical moments concerning her skirt size. She also wears white-blue striped socks and keeps a green strap bag which she keeps near her at most times.

Personality
Lamia's personality is that of a bratty child, as she often acts violent towards the likes of Furuichi. She's been called a 'tsundere' by him. Like her boss, she can read minds, even baby Beel's, although she does not do it very often. She disapproves of Oga as Beel's parent, but reluctantly accepts it after his battle with Tōjō. Although she seemed cold and hostile upon their first encounter, she thanks Oga for saving her after the incident in the demon world. She is very protective of Baby Beel and greatly respects Hilda, whom she refers to as "Hilda-nee-sama."

Lamia has also shown a sadistic side to her personality, showing she had no qualms at the thought of drugging Tatsuya Himekawa and Hajime Kanzaki knowing they would die from the after effects. She expresses her disappointment when Furuichi often foils her plots in drugging the other Ishiyama students.

Tōhōshinki Arc
She is first Introduced after Oga's first fight with Tojo as the Dr. Rachmaninorr's assistant who's going to help Beelzebub to get healthy again.

Prince En Arc
Lamia returns to the human world to take care of Oga's wounds after his confrontation with Hecados and the other demons.

Mobichi Arc
Lamia frantically searches for Hilda in the Oga residence and eventually finds her doing laundry. Lamia immediately asks about the tissue packet that was sent from the Great Demon Lord not long ago and asks that they be returned, explaining that Doctor Furcas said not to use it at all. She then explains more through a demonstration with regular tissues, telling Hilda that sticking two rolled-up pieces of tissues stuffed in one's nostrils can summon a powerful Demon. Lamia is then told that Furuichi, who currently has the tissues, will likely not use them in such a manner; thinking that it might be true, Lamia laughs along with Hilda.

However, the two end up going to Saint Ishiyama Academy to see whether everything is actually fine. They find the homeroom for the Ishiyama delinquents and discover that Furuichi has already underwent the summoning ritual; upon this revelation, Lamia sighs with disappointment about Furuichi. Suddenly, Yuka and Chiaki begin handing Lamia candies while fawning over her; Lamia fruitlessly tries to push them away.

Lamia and Hilda end up going to the rooftop of one of the school buildings with Oga and Baby Beel; there, they explain about the Demonic tissues that Furuichi has been using.

Just as they finish explaining, Lamia spots Furuichi in the hallways while she sucks on a lollipop. The group then observe him from afar, watching as he arrogantly provokes several of the Tōhōshinki into fighting him. Lamia also recognizes the Demon that he has summoned, Hecadoth; Lamia also recognizes Agiel after she is later summoned by Furuichi. While Lamia continues to watch Furuichi fight against Kanzaki and Himekawa, she notices that Oga is having fun at watching his best friend make a fool out of himself; eventually, Lamia berates him for his indifference to the actual problem, but she is then told that he will take care of Furuichi in the end. Eventually, the group watches as Furuichi summons Jabberwock, who ends up helping him defeat Tōjō. After this event, Lamia explains more about the toxins in Furuichi's Demonic tissues. After she finishes explaining, Oga and Baby Beel leave.

Lamia and Hilda later go to the local river just as Oga and Furuichi prepare to have a fight. Unexpectedly, both teenagers start by taking an awkward battle stance followed by a long conversation on which past event was the first time where they fought against one another; annoyed, Lamia and Hilda both mentally tell the boys to start their fight. Sure enough, they do, while the girls watch from afar. Lamia is surprised to watch as Furuichi continues using his tissues one-after-another up until he summons Behemoth, which stuns Lamia. At that point, the fight becomes more intense; when taken to the river's waters, they end up pushing the water away from them, astonishing Lamia. The two then start running closer towards the river to see what is happening near the end of the battle. Eventually, the fight ends and both teenagers collapse from exhaustion on the mainland.

Afterwards, Lamia places a treatment Muumuu on Oga and then Furuichi. After placing one on Furuichi, he awakens and tells Lamia that he dreamt of when he was a child; somehow angered by his words, Lamia hits him across the face and tells him that she will tend to it. She then looks down upon Furuichi as his treatment continues. She later notices that Oga has woken.

Moments later, she sees a group of delinquents appear with the motive to fight Oga. Concerned, she yells at them but silences her voice when she sees Oga stand up against them.

Afterwards, the delinquents from Ishiyama arrive and take care of the trouble altogether; by then, Furuichi has healed up. Lamia then watches as her patient apologizes continuously to his seniors just before being challenged to a fight; upon the latter, Lamia states that he is in no condition to. Her words are misinterpreted by the girls of the Red Tail who immediately assume that Lamia and Furuichi are "playing" doctor, embarrassing Lamia, who also yells at Furuichi to lie back down. Fortunately, the issue is shrugged off shortly after and Lamia ends up watching while the delinquents all have a moment together.

Lamia later walks alongside Hilda, Furuichi, Oga, and Baby Beel at the end of the day. 

Return to Ishiyama High School Arc
One snowy day, Lamia accompanies Furuichi to Oga's house in the Human World. The two encounter Kanzaki and Aoi on the way over; as it turns out, both of the Tōhōshinki are also on their way to Oga's house. Lamia, who already knows why they are heading to see Oga, tells the three teenagers that Hilda will be explaining to them about the King's Crest.

The four then go to Oga's house together where they are greeted by the delinquent's older sister, Misaki, who happily welcomes most of them inside. Misaki then takes them all up to her younger brother's room.

A video call is then set up through Oga's television set which Lamia explains is a natural form of communication in the Demon World. As Lamia drinks to her hot chocolate, she sits in throughout Hilda's explanation. Aoi flusters with embarrassment during the explanation following the "lifelong allegiance" part of the King's Crest; Lamia teases her about it by comparing the bond to that of wedding vows. When Kanzaki inadvertently makes Aoi sulk after Lamia's remark, Lamia scolds the male delinquent.

While she is in the Demon World, Lamia learns from members of Behemoth's 34 Pillar Division that Furuichi was in danger; worried, she goes to help him. Before she goes to Ishiyama High School, she pays a visit to both Kanzaki and Aoi, waking them up and telling them to go help Furuichi.

Lamia and Alaindelon both arrive at the high school together where they discover Furuichi lying on the ground, his heart entirely pulled out from his body; the two immediately break down into tears upon seeing him in such a state. Oga then explains to them about what had happened with Furuichi and his "soul". Lamia becomes worried upon hearing that, knowing full-well that Furuichi would die anyway from his fatal wounds if his "soul" was somehow brought back to his body before sunrise. She thinks about who will be able to treat his wound until Oga says that he will leave it to her; although hesitant about performing such major treatment, Lamia agrees to do it for Furuichi. She tells Alaindelon to take Furuichi somewhere sanitary so that she can help him. Before they leave, Lamia tells Oga that she called in people to help him fight. 

Powers & Abilities
Lamia carries a pistol loaded with bullets containing demonic concoctions that can erase memories, force a person to do one's bidding or, in the case of Oga, trap him in a psychic loop. She is always accompanied by two small Muumuu pets, one of which sits atop her head and often mimics her mood.

Furcas Rachmaninoff
Lamia is Doctor Furcas's assistant, as he is a doctor and Lamia is a nurse.

Hilda
Lamia has a great amount of respect for Hilda. She often praises Hilda and occasionally comments on the latter's beauty, even making positive remarks on Hilda's bust size. She also refers to Hilda as Hilda-nee sama

, meaning "big sister", or Hilda-sama, which is a very respectful way of calling a person.

Beelzebub
Lamia has great confidence in Beelzebub, as she is seen crying and wishing him good luck when she is returning to the Demon World.

Tatsumi Oga
At first, Lamia finds Oga to be disgusting due to his relationship with Hilda. When Oga refuses to believe Lamia is a doctor, she kicks Oga below the belt. She has low expectations of Oga, but Oga's will and his strong connection with Beelzebub during a rematch with Tojo (which Oga won) changes her view of Oga. Interestingly, Lamia expresses a tsundere attitude with Oga.

Takayuki Furuichi
Furuichi and Lamia have a bit of a close relationship. In the beginning, they were just acquaintances, but after playing along with the game along with Yuka Hanazawa, Chiaki Tanimura, Nene Ōmori, Tatsuya Himekawa, Shintarō Natsume, Takeshi Shiroyama and Hajime Kanzaki their relationship grew. (Though Furuichi calls himself a lolicon while walking around with Lamia due to her child-like appearance).

In Chapter 101, Lamia was seen hugging Furuichi when they won the game. En, who likes Lamia, seems to be jealous of Furuichi at times because they are close when he sees them. Some perceive Furuichi as a lolicon after he and Lamia are caught in a lewd conduct when Beelzebub and Oga level Himekawa's home or the time when Honoka sees him and Lamia together. Lamia often clings on to Furuichi when nervous or scared.

She does show a lot of concern for his health and becomes extremely worried when he abuses the demonic tissues to fight others. She attempts to berate Oga for laughing at Furuichi when he beat Kanzaki and Himekawa as she is afraid of the toxic effect of the tissues on his body. Once he is defeated by Oga, she tries to protect him from being bullied by Tojo, Kanzaki and Himekawa who wanted revenge.

In the side story of the main series, Furuichi returns to the demon world in order to assist in a mission. Upon reuniting with Lamia, it was shown that she had developed romantic feelings towards him. When Furuichi and Lamia travel back into the past through their linked memories in order to assist Athrun regain his memories, their meddling in the events accidentally alters the present, resulting in Lamia gaining stronger feelings of attraction towards Furuichi than she already had.

En
It can be implied Lamia once acquainted herself with En in the past, she claims she is not very good at "dealing with him" because every time she is near him, he gets shy and territorial about her, which greatly annoys her. En adresses Lamia as his "wife" much to the her annoyance.

Laymia
Laymia is Lamia's mother.

Trivia

 * In the manga, Lamia's carries a pistol with her. This is altered to look like a toy gun in the anime because in Japan, citizen gun ownership is illegal. Not to mention her child-like appearance.
 * Her name is a reference to the Lamia, a creature from Greek mythology that is known to have a female upper body topping a serpentine tail.
 * In the Beelzebub Bangai Hen (side story) series, Lamia is confirmed to have romantic feelings towards Furuichi.