BTVS: TALES OF THE SLAYERS
It has been centuries since the last Slayer was called. Demons were banished from the Earth at some point in the 21st century by an unnamed Slayer and her friends, and the Watchers' Council has descended into a group of crazed fanatics. The vampires however, now dubbed lurks, have returned and haunt the city. In order to combat this threat a new Slayer is called: a professional thief named Melaka Fray. With the Watchers' Council ineffective, a group of "neutral" demons send the demon Urkonn to prepare Melaka Fray for the war that is to surely come.
Although training hard and feeling confident, Mel finds herself out of her depth when she fights a vampire she once encountered in her youth, named Icarus. Years before, Icarus had severely injured Mel and killed her twin brother, Harth. However, Mel discovers that Harth was not actually killed, but after being bitten by Icarus, he bit back and fed off the vampire, becoming a vamp himself. Since he was the Slayer's twin, he had had the visions and instinctive knowledge that should have been hers- he knew what Mel was long before she did, and also knew how to become a vampire.
Disheartened, Mel refuses to fight, until she discovers the body of her young friend, a mutant girl named Loo, with her neck snapped. Determined to avenge her, Mel rallies the inhabitants of the slums to fight against the Lurks. Mel's older sister convinces some of the local law enforcement to also join in the crusade.
As the battle begins, a giant dragon-like demon flies over the scene. This, Urkonn tells Mel, is the gateway to the demon world, and thousands more demons will appear from it. Mel deliberately allows herself to be eaten by the creature, before killing it from inside by stabbing its brain. She climbs out of the creature and again encounters Harth, riding on its back. His plans foiled, he does the one thing she never expected- kisses her and runs away.
The world is safe, but one more order of business remains- Mel tells Urkonn that she knows a Lurk couldn't have killed Loo- they couldn't have got into her flat uninvited, and would have drained her blood, not snapped her neck. She knows it was really Urkonn who did it, hoping to inspire her to fight. Having figured out that her demon mentor can't swim, she drops him into a pool of water and kills him.
Melaka returns to her former life of crime, while at the same time killing any Lurks she finds. In another world Urkonn's superiors state that he will be stricken from history for his failure to kill her after she stopped Harth, and start to discuss their plans for when Harth tries something again.