Warning! This includes spoilers Slayers Up to the end of Try as well as parts of my own story. It is recommended you read it along with Trickster Children 4: Mother-In-Law. Also, as this is a story in progress, these descriptions are subject to change at whim.
Anime: Xelloss is a Mazoku which means evil race. The mazoku are the basic force of evil in the Slayers world and seek to cause chaos and destruction where possible. Xelloss is the Priest (and maybe General, I've heard both ways) of Zelas Metallium and is one of the most powerful mazoku there is, second only to Shabranigdo and the 5 Dark Lords. Xelloss is well known for his cheerful smile and closed, happy eyes which hide a mind full of secret plans. His true form actually resides on the astral plane and is, in fact, a giant black cone! His most famous line is "Sore wa himitsu desu." which means "That is a secret." He spends Next following Lina and the gang around and subtly manipulating them. During Try his goal is to convert or kill Valgarv, and then later to help save the world because "We want to destroy it ourselves, and we don't need any help from some outsiders."
Trickster Series: In Trickster's Wedding I make the assumption, based on evidence from the anime only, that Xelloss not only CAN have emotions but that he has a thing for Filia which he has a really hard time admitting at first (see arguments section for further evidence from anime). As the story progresses I allow him to grow as a character and accept his emotional side a little more. Though being a mazoku he will always have a little trouble with it. And he will never cease to enjoy annoying Filia no matter how much he may love her.
Filia Ul Copt
Filia Ul Copt is introduced as a Priestess of the Fire Dragon King. She is a Ryuzoku (Dragon race, which are the opposite of the mazoku and are the force of good in the Slayers world. Filia starts out very idealistic, but over the course of Try she comes face to face with reality and learns to accept it. She is very energetic in pursuit of her missions, but also has a whimsical side with her obsessions with true love, sting games and, most of all, tea and pottery. Filia's natural form is a large golden dragon, but she can take human form though her tail sometimes pops out when she's agitated. She also carries a very heavy spiked mace on her garter and will flip up her dress and take out the mace to threaten those who annoy her.
Trickster Series: By the end of Try Filia had given up her position as a priestess of the Fire Dragon King and her clan was annihilated soon after. Valgarv was also killed and was reborn as an egg which Filia adopted. I assumed that only the Fire Dragon people were killed. This means that Filia lives on her own without others of her kind, but Golden Dragons (such as the Saichuro of the Earth Dragon people who acts very similar to the Fire Dragon's) can occasionally appear and are from other clans. After adopting Val's egg Filia opened a pottery and Mace shop with the help of Jillas and Grabos. She was traveling with the rest of the cast in Trickster's Wedding because she missed her friends, and she was a little bored waiting for Val's egg to hatch.
We know relatively little about Zelas from the anime. She is a Dark Lord, one of the 5 serving Shabranigdo. She is Xelloss's master and the real mastermind behind his schemes. She is Called Juo-Sama or the Beastmaster and has two forms, one resembling a wolf and the other a beautiful, scantily clad woman who smokes and drinks wine. Trickster Series: All of Zelas's personality in my stories is extrapolation. She is involved, behind the scenes, in a massive amount of intrigue and manipulative scheming so I had her apply that scheming to Xelloss, choosing to find a use for her minion's irresponsible infatuation with a dragon rather than get upset about it. She acts very calm and in control because usually she is. She is aware of far more than she lets on and has no qualms with using anything, including her own grandchildren. But, like Xelloss, she can be susceptible to emotions, much as she will deny it and some inherent fondness for certain individuals can have an effect on how she decides to use them.
Show: Valteria was an ancient dragon who was nearly killed during the genocide of his race by the Golden Dragons. This genocide was the result of conflict over Garvera, the most powerful of the weapons of light. Valteria was left wounded and dying until he was approached by Garv, the Demon Dragon King, a mazoku lord. There had been some falling out between Garv and Fibrizzo, the Hellmaster and most powerful of Shabranigdo's 5 Dark Lords. As a result Garv had been banished from his people. He sought out Valteria and offered, that if Val would serve him he could save him b transforming him into a mazoku. Valteria agreed and was renamed Valgarv becoming Garv's general. After Garv's death he seeks out Lina and Xelloss in vengeance and becomes involved in the Otherworlder's quest to collect the five weapons of light and defeat Darkstar. Valgarv initially works with the otherworlders in exchange for a promise of help with his own quest. However, he becomes frustrated by Almace's concern only for his own mission, and he turns against everyone joining with Darkstar to destroy the world, so that it can be purified. He is defeated, in the end, by a combined effort and is reborn as an egg which Filia takes to care for.
Trickster Series: Val hatched approximately two years after the end of Try, one year before Xelloss and Filia's twins. He was reborn as a full ancient dragon, and has very little memory of his old life. However he has a lingering mistrust of the mazoku, and golden dragon races in general with the exception of his foster parents. He realized early on that he was adopted (the fact that he was an ancient dragon and his "parents" were a Golden dragon and a mazoku was a big clue.) He stubbornly refuses to take the name Metallium insisting on keeping his old name in honor of his murdered people. But in spite of his fierce independence he gets along well with his foster family. Filia especially makes every effort to see that he is included. He is fairly protective of his younger 'siblings' becoming very upset if anyone tries to mistreat them because they are 'freaks'. He will often play along with the twins various pranks but will occasionally play the role of annoying eldest trying to make them behave, usually resulting in a typical sibling fight, only these siblings all tend to cause more than a typical amount of damage. He at times finds himself asking "Why me??" especially when Zelas shows up and instigates things with her blatant favoritism towards her 'Darling Grandchildren' but the twins always make it up with him and things return to normal.
Adrianna Violet Metallium
Xavier Bronwen Metallium