There are two of these sequels to the Record of Lodoss War anime series. Legend of Crystania: The Motion Picture, and Legend of Crystania: the Chaos Ring. The first is a film, the second is a three-part OVA presented as a single film. Both films follow the same characters on the island of Crystania (the god-land north of Alecrast, which itself is north of Lodoss Island), centering on the plight of Ashram, who has been taken over by the dark god Barbas, and Pirotess (which is pronounced Pirotessa in this film for whatever reason, though she is usually called Sheru) as she attempts to rescue him.
Some quick history is needed to really explain the plot of these films. It will also slightly spoil the end of Record of Lodoss War, so read this part at your own risk.
At the end of Record of Lodoss War, Ashram and the people of Marmo are left without a home. His ambitions of ruling a united Lodoss crushed, and his island being overtaken by the impending resurrection of Kardis, he gathers his people onto ships and sets sail for a new land.
During the War of the Gods (the same war in which Marfa and Kardis fought and Lodoss was created), many of the gods escaped to Crystania where they took on the form of animals and created a new land. They shut this land away from the rest of the world, allowing no outsiders onto the land. Races of shape shifting beast-men were created to populate the land, each race corresponding to a beast god.
At the beginning of Legend of Crystania, Ashram has traveled to Crystania, having found no other place to go. In order to secure a new home for his people, he makes a pact with the evil god Barbas, who takes control of his body. Ashram goes into a deep sleep inside his own body for 300 years.
After the 300 years, the immortal Pirotess still searches for a way to free her love from Barbas. Although this is a main driving force of both films, neither Pirotess or Ashram are the traditional main characters. The story focuses more on a young man named Redon, who, to save time, is basically this time period's Parn. After a messy (but successful) assassination plot against his father, Redon escapes with his loyal friend (and servant) Kwairde. They escape to Crystania, and are let inside, followed by several others from Lodoss: Obier (his father's would-be assassin), Raifan (a young shaman in training), Nasare (a sorceror), and Aderishia (a priestess). Along the way they meet up with Pirotess and some of the beast-men, and together fight to release Crystania and Ashram from Barbas' power; while conquering their own personal demons, of course.
The Chaos Ring is a direct sequel and picks up right after the first film (well, some time has passed, but nothing significant). There's some more back history in this one; the first film does little to explain the creation or significance of Crystania, but before each episode the history is explained (much like in Lodoss War). All of the animal gods make an appearance this time, not just Barbas. This time Barbas is attempting to regain his power and become the God's King, ruling not only Crystania itself, but all of the other gods (who jointly reign). The group, which had split in the interim, is called back together (or reforms along the way), to save Crystania once again, with plenty of brand new dangers.
For people who are thinking: Why is Ashram suddenly a good guy? He isn't suddenly anything. Ashram was never a bad guy. His intentions have never been evil. Antagonist does not always equal evil. Sometimes characters have the best intentions but use the wrong methods. Ashram was rather cold at times and did on occasion use very deadly force (which is in part due to the orders of his emperor (who had unfortunately been corrupted by the Demon King) , and the demon sword he also eventually carries), but all he ever wanted was a home for his people. And on his own (without the influence from Emperor Beld), he's a fairly honorable guy. He is changed from his character in the Lodoss series to an extent, though most of it is a visual impact (negatively); he also has more open feelings now, notably toward Pirotess, though his love and duty for his people has not changed (it's actually amplified). Regardless, his actual role in the films is quite small.
If you really must have more Lodoss, or you're interested in the mythology as a whole, then it won't hurt to watch these films. But if you're looking for a good anime, then you should stay away (unless you are really into sword and sorcery). Both films are poorly animated, acted, and written. There are plot holes between the two, pronunciation discrepancies between the dubbings of Lodoss War and the Crystania films (Pirotess isn't the only one with a new pronunciation), and the new characters are mostly uninteresting and have little personality. Redon is basically a copy of (young) Parn, but with no one like Kashue around to whip him into shape; there's something about him that several characters keep referencing (like within his soul, or his destiny), but nothing ever comes from this. Nasare isn't even half as interesting as Slayn. Aderishia could be really interesting too, but like Redon, most of her potential as a character goes unused. Pirotess doesn't even feel like the same character most of the time, and her and Ashram's character designs are plain and a little drab.
Both films are available from ADV Films.
Image (top to bottom, left to right): Obier, Raifan, Aderishia; Nasare, Redon, Pirotess/Sheru; Kwairde.