Thetis

is the daughter of Holy Knight Golgius, and Queen Elizabeth's personal magician and the best one currently serving the Kingdom of Liones.

Chaos in Liones arc
Thetis remains inside the castle as the battle against Arthur Pendragon takes place, when Queen Elizabeth fears that something dreadful is happening, Thetis suddenly laughs as she feels Lancelot's arrival to the fight much to the Queen's confusion.

On the night after the battle, Lancelot finds Thetis in front of Melagaland's corpse. Lancelot tells her that she is weird for praying for the deceased Galand and Melascula who killed thirteen people, to which Thetis replies that she only feels sorry for them and then corrects him that it was twelve people. Thetis reprimands him for allowing Jericho to kill the prisoner who was their only foothold to get to Camelot, to which Lancelot excuses himself by saying that he could not lift the magical restraint Thetis placed on the prisoner. As Lancelot say that she does not understand how he feels and calls her an old hag, Thetis reminds him that they have the same age and that he does not understand her feelings neither, since reading minds and understanding feelings are two very different things. Thetis teleports away, calling Lancelot a "brat" and to cool his head with a night breeze.

Wallnack arc
Thetis is present during the audience between Percival's group and the king. She introduces Elizabeth as the Queen of Liones and gets annoyed by Meliodas's actions.

She then participates in the meeting in the war room to discuss the situation with Camelot. Thetis reprimends some of the attendants for being noisy and urges Meliodas to get started. When Anghalhad ask why are they fighting a kingdom that was destroyed 16 years ago, Thetis explains that Camelot was recreated in an alternate dimension by the power of Chaos but are now starting this war because there is a price to pay in order to rebuild and maintain the new Camelot. To further emphasize her words, she uses her magic to show everyone to a landscape that has been stripped of various parts, leaving only empty spaces.

Thetis says that the erased mountain used to be a premium quality ore and that it was surrounded by forests, lakes and many small villages, such as Ordan, Cebron and Igor. When Percival says that they must go to Camelot to stop Arthur, Thetis recites the prophecy spoken by Bartra Liones that when the Four Knights of the Apocalypse are reunited, their hope will be lost at the hands of a Chaos assassin and the sword of a traitor. Thetis explains that although an omen is not an ability to see the future with accuracy, it is an essential power to take the initiative against Camelot, which led them to believe that the enemy was after Bartra, although in reality their objective was the prisoner of war that was to be used as a key to Camelot, who was killed by a former Holy Knight of Liones, Jericho, after seeing that she could not free him from the magical restrictions that Thetis placed on him. When Donny and Percival ask Meliodas why he did not go to Camelot himself while he could instead of waiting for the Four Knights, Meliodas replies that he could not because he is a demon, leading Thetis to explain that Camelot is protected by a barrier that prevents any race except humans from entering. As Meliodas says that they entrust everything to the Four Knights of the Apocalypse for being humans and half-humans, Thetis says that it is normal that Camelot's barrier does not affect half-humans since it has never been heard of before to have beings born from two different races and also including any more specifics would have reduced the defensive capacity of the barrier. When Tristan interrupts her to point out that they are at a dead end by not being able to go to Camelot, Thetis and the rest can not come up with a solution, leading Percival to suggest they just go on an adventure to find one.

Tethis comes to Wallnack to take care of Jade's dead body. She laments that they took a casualty so soon, vowing to take responsibility for the body and return it home. Tethis tells Tristan that they should keep looking for clues about Camelot, but Tristan reveals that they already got solid information from Ioladio.

Abilities/Equipment
Thetis is a very skilled magician, enough to be appointed as the queen's personal one.
 * High-level teleportation magic that allows Thetis to appear and disappear at precise locations and teleport groups of people instantaneously.

Weapons

 * Staff

Lancelot
Thetis and Lancelot seem to know each other for some time, engaging in banter and calling each other names, as well as acknowledging each other's abilties. Thetis is shown to be briefly annoyed with Lancelot not being able to stop Jericho from killing the prisoner and taking their path to Camelot with it.

Golgius
Not much is shown about their relationship, but it is shown that they care deeply about each other. Thetis promises her father that she'll be there for him, while her father tells her that he prays that she'll find the "star" that she's looking for.