Selene is a female Moon Dragon and member of the Five Dragon Gods of Guiltina. Referred to as the Moon Dragon God, Selene has the ability to cross dimensions, and is able to cross between different worlds.
As a dragon, Selene heavily resembles a Kitsune fox, with a furry head, neck and back. The fur runs all the way to the tip of her long, sinuous tail along her spine. Like a Kitsune fox, she has eight additional, foxlike tails on her back above her hind legs. Her face is likewise very foxlike, and she has a set of mammalian ears and a ruff of fur which transforms into hair when she becomes human. Her fur and scales are white while her belly is a darker blue shade. The tufted tips on her tails are dark black. Her horns also are long and sharply pointed, sweeping backwards, with blackened tips, and like all dragons, her mouth is filled with razor-sharp teeth.
As a human, Selene takes the form of a buxom, curvaceous and beautiful human woman. She has long white hair extending to her hips, which transforms into her furry ruff when she becomes a dragon. For attire in human form, Selene wears a loose kimono with fur lining on the top while also having flower designs all over it as well as zigzag lines on its edges. The kimono itself is very revealing, exposing her legs to about mid-thigh and leaving much of her chest uncovered. The back of her kimono has another layer of cloth with no intricate designs. Her head is covered by a hood adorned with an upward crescent moon with a gem on top as well as a pair of wings on each side. She wears a pair of socks while wearing wooden sandals.
Selene utilizes Moon Dragon Slayer magic. With this ability, she can draw power from the moon and stars. Her powers also allow her to cross between the three interconnected worlds of EarthLand, Edolas and Elentir. As a result, she is known in all three worlds as "the dragon who can cross dimensions". Her powers also allow her to create an artificial moon as well, which she can use to cross between worlds.
Selene's power is only rivaled by a few others; among these, only the other members of the Five Dragon Gods; Ignia, Mercphobia, Aldoron, and Viernes are her equals, and her strength rivals if not surpasses the Black Dragon of the Apocalypse himself; Acnologia, whom she once feared.
Selene is deceptive, alluring, and manipulative. Pure evil, she revels in people's fear of her when they can sense her power, and she uses this fear to coerce them into doing her bidding. She also dislikes the other Dragon Gods, as she readily would prefer to get rid of them so she can achieve world domination. However, she is far to cunning to rush into battle blindly. She knows full well that attacking the other Dragon Gods could result in her death as much as it could result in her killing them. To that end, she intimidated Faris, a White Wizard from Elentir, into traveling to Earth-Land to erase Mercphobia's magic power in order to remove any threats to her plans. This plan worked on making her control Mercphobia, but resulted in Faris awakening Aldoron from his slumber, which Selene wanted in order to make things more interesting and to allow Selene to use him as a weapon to kill the other Dragon Gods. She was genuinely surprised by Aldoron's defeat, but saw it as an opportunity to face Aldoron's killer, Natsu Dragneel, and take over the world herself. When she faced off with Natsu, she decided that she would toy with him first before actually trying to fight and kill him, and so transported him to Elentir with his team to begin her "game".
To be succinct, Selene is a sadistic and wicked individual that takes delight in people's suffering, among other things. She cares nothing more than to see endless chaos and destruction as it brings amusement for her. As part of her sadistic nature, she goes out of her way to manipulate Faris into doing her bidding by threatening to take Elentir away from her if she does not do as she is told. Like Aldoron and Ignia, she thinks highly of herself above all others, but unlike them, she thinks she's above the Dragon Gods themselves even, as she considered Aldoron to be weak when he had been killed by Natsu. She also seems to have somewhat of an indecent nature to her as she doesn't mind bathing herself in front of Natsu and Gray while they were held captive.
Despite this, however, she seems well aware just how limited she is if she were to fight the other Dragon Gods. While she believes she could kill one of them, she might die in the process, which is something she does not want to risk. She also acknowledged Natsu to be someone worth of her time and because of his status as Ignia's brother. Selene also believes the days of dragons are over, and instead desires to live in her human form and reign supreme as the strongest wizard in the world. To further this goal, Selene decided to take over the wizard guild Diabolos after killing its master and become its new guild master. This suggests she may have more of an appreciation for humanity than assumed, or at the least, she enjoys their adulation, awe, and obedience.
In spite of her wickedness, Selene was capable of showing love, at least to a few other people, such as her dead son, the Sword Saint Dragon, Kurnugi. She willingly let herself be subdued in battle by the Dragon Slayer Suzaku as a means of getting close to the guild master of Diabolos; Kurnugi's murderer, Georg Raizen, whom she quickly and brutally crushed in vengeance.
Selene was born at least 400 years before the events of Fairy Tail: 100 Years Quest. In that time, she hat at least three children, one of whom was Kurnugi, the Sword Saint Dragon. Some time after giving birth to her children, she and the other Dragon Gods fled from Ishgar when Acnologia began his genocide of dragons during the Dragon King Festival. In the years after, Elefseria, the founder of the first wizard guild and a Dragon Slayer-turned Dragon, tried to defeat her, but was unable to do so because of her vast power.
Selene was mentioned by Mercphobia after Team Natsu defeated him and sealed away his power. Mercphobia knew very little about her as he never met her personally when warning the team about her.
Selene was responsible for causing the overflow of magic power in the alternate world of Elentear, where she made heir base on Black Moon Mountain. She commissioned and strong-armed White Wizard Faris into doing her bidding to erase the magic of Earthland and help her destroy the other Dragon Gods. To that end, Faris took control of Mercphobia's magic and then tried to control Aldoron to fight the other Dragon Gods, though Faris was eventually defeated and redeemed when it was revealed that Selene had manipulated her. Mystogan, king of Edolas, would reveal Selene was able to cross dimensions and that she was the reason Edolas' people never harvested magic from Elentear. Selene herself would appear after Faris told Team Natsu about her, wounding Faris and briefly battle Natsu before transporting everyone to Elentear. There, she let her three servants, Mimi, Yoko, and Hakune, the three Moonlight Divinities battle and defeat them before transforming the female members of the group (Lucy, Erza, Wendy, and Carla) into monsters before letting Natsu Dragneel and Gray Fullbuster, battle them at the bottom of Black Moon Mountain.
During this battle, Selene was confronted by the Dragon Slayer wizard Suzaku of Diabolos, who challenged her to duel after defeating Natsu and Erza in short order. Suzaku and Selene's battle proved so fearsome that Mercphobia could even sense it between dimensions. During the battle, Selene recognized Suzaku's magic was that of her son, the Sword-Saint Dragon, Kurnugi, whose flesh Suzaku had eaten after Kurnugi had been killed by Georg Reizen, the Guild Master of Diabolos. The Dragon Slayer eventually gained the upper hand, severely wounding Selene and causing her to try and escape through a dimensional portal back to Earthland. Suzaku promptly caught her before presenting the now-chained Selene to Georg, who was surprised and delighted to learn that one of the dragons he had slain had been her son. Attempting to attack her after she transformed, Georg Reizen was promptly crushed beneath Selene's foot, and the other members of Diabolos could only stare in shock due to how strong and fast she had revealed herself to be. Selene then offered Diabolos' members a choice; fight her and die, or let her lead them as Diabolos' new Guild Master. Realizing the folly of fighting her, Diabolos' members quickly submitted to her leadership.
With her dominance established, Selene ordered her new guild to enter the Great Labyrinth of Dogra, where the bones of her fellow Dragon God, Dogramag, lay entombed in order to claim a weapon that would help to defeat the other remaining Dragon Gods, Ignia and Viernes. This weapon, the heart of Elefseria, contained all the knowledge of magical weapons needed to potentially kill the Dragon Gods. Upon her arrival, Selene's forces entered the labyrinth, while she waited at the entrance for Elefseria and Team Natsu. She then challenged them to a "game"; if their guild could beat hers and bring her the heart, then she would release Elefseria, whom she took captive. Reluctantly agreeing to her terms, the group entered the magical labyrinth and did battle with her forces, eventually defeating most of them. However, when Ignia appeared, Selene was left with no choice but to enter the labyrinth herself and stop him.
Using her dimensional transmission abilities, Selene tried to ambush Ignia when he found Elefseria's hear, but the Fire Dragon God was quick to counter her. Ignia deduced that Selene had sided with humans and Selene in return stated the age of dragons was over. Ignia, not wanting Selene to use the heart's store of knowledge to try and destroy him and Gold Dragon God Viernes, then burned the heart to ash, much to Selene's shock and dismay. Both dragons then transformed from their human states into their dragon forms, whereupon they prepared to do battle at last.
Ignia and Selene quickly began to trade blows, damaging the labyrinth further, and employing every trick at their disposal. Selene initially thought she had the upper hand, but even with her magic to help her, Selene was heavily damaged by Ignia's flames, while Ignia was himself showing little in the way of exhaustion or injury. The fight caused Natsu, Suzaku, and Natsu's exceed friend Happy to stare in shock and amazement when they stumbled onto the battle. However, for Natsu, the fight caused flashbacks of his father's death and Natsu screamed for the two dragons to stop fighting. Selene was appalled at why he wanted the fight to stop, especially since the death of one of them would end up giving Natsu and his friends one less enemy to fight, but Ignia knew that Natsu did not want to see a repeat of Igneel's death. However, Ignia told Natsu that he was different from their father, and stronger than Acnologia, before sending a full-powered Fire Dragon Roar through Selene's neck, causing her to spew blood from her mouth in agony. Shocked and horrified by the underhanded blow his brother had delivered, Natsu shouted Ignia's name in rage as his companions looked on in terror.