When Lina destroyed Phibrizo in Slayers NEXT the barrier he created that surrounded Seyruun was dispelled along with him. Now there is a whole new territory just waiting to be explored. Lina and Gourry are in Seyruun to see what all the fuss is about when Lina receives a letter from a mysterious person named "Filia" requesting an audience with her. They bump into Zelgadis who is there to go to the new land to see if he can find his cure. Zelgadis stays with them and they meet a lovely blonde woman, Filia. She acts very discreet and mysterious but that is over when Gourry notices a "tail" underneath her dress. Gourry being the oaf that he is looks under Filia's dress to get a better look. This enrages Filia and she whacks Gourry with a mace hidden under her dress, and then runs off crying.
After that they spot Amelia who is being sent as an emissary to the new land. Just as they are about to speak to her the harbor is under attack by a Golden dragon. After trying to avoid the destruction the Slayers realize it is not the town the dragon wants to destroy but they themselves. They manage to get aboard the ship to lure the dragon away from the town so as not to cause any more damage. While out at sea, Lina casts the Dragon Slave causing a huge tsunami, ironically missing the dragon completely. Deciding to stay on the slightly damaged (okay maybe not "slightly" damaged) ship the Slayers go off to the new land to see what kind of trouble they can get into.
After running into trouble with some beast men they once again come across Filia who revealed that she was the Golden dragon who attacked them in Seyruun. She was sent from her temple to find the one who has enough power to save the world from destruction that was foretold in a prophecy…
"Those who control the evil stars shall be led by the light and will hide the world in darkness. Dragon blood shall cover the world leading the power of light and dark, revealing the stars. The power of those stars shall be darker than twilight and brighter than sunrise. When at its peak, it shall become a streaking arrow that will pierce the heavens."
Lina thought the idea of her being the world's savior was ludicrous but then was angered when Filia said that she was the second choice for the job. There is another who is even stronger than Lina but they declined the offer and suggested that Lina should do it. They also sent Filia with a letter instructing her to give it to Lina when Filia finds her. Lina read the letter only to become terrified enough to build herself a tomb. The letter simply said, "Just do it! Love Big Sis!" Lina's older sister Luna was the first choice but was too busy to do it so she ordered her little sister to take on the job. Lina who is terrified of her sister and knows she cannot disobey her agrees to go with Filia on her quest.
On their way to the dragon temple Lina needs to get a bite to eat much to Filia's dismay. The group splits up along with Xellos showing up and playing a few tricks on his old companions. Then do not seem to notice it is him however but when they regroup Lina spots a shadowy figure that she seems to recognize. After following him she concludes that it is Xellos. They all begin to think that this is something serious if the mazoku are involved. All of a sudden they are attacked by a mazoku who came out of nowhere. He explains that is Valgarv who was a minion of Garv and wants to have revenge on Lina Inverse for killing his beloved master.
As Valgarv begins another attack, Xellos shows up and helps Lina and co. out by taking up a fight with Valgarv. While this is going on, Valgarv's minions lure Lina and the others into a trap by attacking a nearby village to rob them of their holy relic. They are surprised to find the same beast men they had fought earlier and that Valgarv possess a light weapon that is similar to Gourry's sword. As they fight their weapons clash causing an astounding reaction that shocks everyone. Then Almayce, a God who is from the Overworld and is working with Valgarv shows up and ends the fight there for now.
After several encounters with Valgarv's minions the finally reach the fire dragon temple and sort of destroy part of it in the process. While they are forced to repair the damage they have done, the dragon elders agreed that Lina was qualified enough to go on this quest. As the supreme elder explains to them what their mission exactly is, Almayce shows up and demands that they hand over the sword of light so he can summon the Dark Lord Dark Star to the Slayers world. Dark Star is the Dark Lord of the Overworld and is the equivalent of Ruby Eye in the Slayers world. Everyone is shocked at this and become even more so when the supreme elder agrees to Almayce's request as long as he summons Dark Star in a different world other than their own.
Almayce concedes but this angers Lina and the rest. It angers Lina and Gourry because the sword of light belongs to them and the others are angry because the supreme elder does not care what happens to the other worlds as long as theirs is safe. They begin to fight and that is when Valgarv shows up. He believed that Almayce had betrayed him and when he tried to attack everyone Xellos stopped him. They continue to fight each other and everyone else goes up against Almayce.
They're surprised to see that spells don't work on him so Lina tries to use the Ragna Blade on him. She only managed to crack his armor a bit but it does wound him. Valgarv enraged by everything attempts to change into his Ancient dragon form but it is too painful for him to accomplish. He teleports just in time before Xellos kills him, swearing that he won't let it end this way.
Now that they know what Valgarv and Almayce's plans are, they set out on their journey to find the rest of the Dark Star weapons. Filia joins them for she wants to find out the truth behind Valgarv's race and to stop Dark Star from being summoned. They search for the final weapon only to be tricked by one of Valgarv's minions, Jillas. He manages to steal the sword of light, for Valgarv only needs that and Ravdomezehis, the weapon he fought Gourry with earlier, to summon Dark Star. They follow Jillas to Valgarv's hideaway where they try to stop Valgarv but he operates a transport of some sort to go to where Dark Star is.
Lina and co. get caught in the beam as well but when they arrive Valgarv is just about to summon Dark Star. Filia tries to stop him and asks him the truth about what happened to his race but he refuses to answer her. He manages to put the two weapons in place and offers himself as a sacrifice to Dark Star who absorbs him. Lina is about to cast the Giga slave as a last resort but is stopped when two shining figures appear before her with two Dark Star weapons which seals Dark Star in a magical barrier. It causes an explosion and everyone is scattered.
After a bunch of random wackiness they meet up with each other again and go to look for the final Dark Star weapon. They finally find it after some misadventures at the temple of the Ancient dragons. While they are searching for the weapon Filia learns the awful truth about what happened to Valgarv's race and that her people were cold-blooded murderers. Meanwhile Golden dragons came to protect the temple from the two Overworld Gods who had sealed Dark Star.
They want the final Dark Star weapon as does Xellos who appeared to be on their side but has his own agenda. He attacks Filia and the supreme elder just when they found the final weapon, Galveria the bow. Their accomplishment was left un-rewarded however, for Xellos stole Galveria after giving Lina a shift blow to the head knocking her out.
Now Lina is really pissed off, so everyone follows Xellos back to where Dark Star is held. After Lina gets back at Xellos they all agree they need to work together to destroy Dark Star. Unfortunately he escapes the barrier and they are unable to kill him as he escapes to the Golden dragon temple. It turns out that Valgarv didn't die but merged with Dark Star. During the earlier battle all the Golden dragons save the supreme elder were killed. Valgarv kills the supreme elder after a heated conversation between the two of them. Valgarv decides he is going to destroy the world to end the endless battle between the Gods and monsters and he will purify it so no mistakes will ever be made again. He again flees but Lina and everyone cannot let this happen so they prepare for the final showdown using the Dark Star weapons.
Filia knowing Valgarv better than any of them knew where he was going so they all follow her to the Ancient dragon temple. There they have the final battle as Lina uses the five Dark Star weapons along with Filia's holy magic and Xellos' mazoku power combined to make the ultimate spell, which destroys Dark Star and sadly Valgarv along with him. Everyone is saddened by the loss of Valgarv for he was the one who needed to be saved from his cursed fate. Filia is the one who is moved by the loss of Valgarv the most for she felt that she was no better than those who killed his kind. When she thought all was lost, Filia saw a tiny orb of light fall gently from the sky. She ran towards it as it came to rest in between her hands, her eyes lit up with tears of happiness as she realized that it was Valgarv reborn as a baby dragon. To atone for her races sins Filia decides to raise Valgarv and give him the happy life he so needed.