The Slayers
Lina Inverse is a 16 year-old sorcery genius who in her travels has already picked up quite a reputation as a bandit-killer, dragon-spooker, and the natural enemy of all who live. She is the master of the Dragon Slave, the most powerful spell known to black magic, as well as a complete assortment of other magics, and a competent sword-user and fast-talker.
As the series starts, she is traveling alone, making money by attacking bandit gangs and stealing their loot. She is rescued from one of her victims turned vengeful by Gourry Gabriev, a tall and gallant, yet dumb-as-a-brick swordsman, who (it is revealed later) wields the mythical Sword of Light, a family heirloom of his that has the power to destroy a monster's astral form.
After several plot twists, they gain a new ally, the mysterious and powerful half-Golem Zelgadis, a swordsman and shamanic magic user who serves primarily as a foil for the goofy antics of the rest of the team, along with a couple of his henchman. They are all trying to stop the High Priest Rezo from curing his own blindness, which he believes can only be done by summoning out the evil spirit within them, which is no less than a piece of the legendary Monster Lord, Ruby Eye Shabranigdo.
Both of the henchmen are lost during the battle, and Lina's Dragon Slave proves useless, since it's source of power is the Monster Lord himself, but the survivors eventually prevail through a combination of the power of the Sword of Light and Lina's secret spell, the Giga Slave, which calls upon the only being more powerful than the Monster Lord - the Lord of Nightmares. The only catch to the spell is that even the slightest error in the casting will destroy the entire world, and even doing it properly can kill the caster.
Needless to say, the spell goes off without a hitch, and Zelgadis goes off on his own journey to find a cure for his chimera body, leaving Lina and Gourry to continue their trip to Atlas City, ...
...which they never reach. Along the way, they meet Prince Philoniel of Seyruun, the city of white magic and his justice-freak daughter Amelia. After resolving some family troubles, Lina and Gourry decide to accompany Phil and Amelia back to their hometown, where they discover that an unknown party in the holy city of Sairaag has place a bounty on them and the absent Zelgadis for the murder of the High Priest Rezo.
They also run into many pursuers, including the confident swordsman Zangulus and the quiet magician Vrumugun, who pursue the team of Lina, Gourry and Amelia (who decides to accompany them for various reasons) all the way to Sairaag. Once there, they confront their enemy, Eris, a former cleric who served Rezo, and is attempting to produce a clone of the dead priest.
The group is saved from certain defeat by Zelgadis, and meet Sylphiel, a powerful but naïve cleric who is in love with Gourry. Vrumugun is finally destroyed, and they confront the clone, put even at partial strength, Copy Rezo manages to destroy the city. Eventually they find Rezo's underground laboratory, where Gourry and Zangulus have a final duel, and they defeated Zangulus points them towards their goal. When they arrive, they find Eris with the fully awakened clone, who kills its creator, and unleashes the power of Zanaffar, an astral beast that was sealed inside the holy tree of Sairaag hundreds of years ago by the Sword of Light.
The ensuing fight is desperate, and Lina is mortally wounded, but resurrected by Sylphiel, who borrows the power of the Blessed Blade, a sword formed from the holy tree itself. Gourry, Zelgadis, Amelia, and a belated Phil manage to make progress, but they are clearly losing until Lina arrives, and uses the Blessed Blade to finally destroy Zanaffar and kill Copy Rezo, who dies content in the knowledge that in his final hours, he was more powerful than his original.
As reconstruction of the city begins, Phil is called back to Seyruun, and Amelia, Lina, Gourry, Zelgadis and Sylphiel all follow for a new adventure.