Denam first encounters Nybeth in Chapter 1 after saving Leonar, who was ordered by Duke Ronwey to hunt down the Necromancer. Throughout the game, Nybeth has only one goal - to be the best Necromancer in the land and find a way to cheat death. He is willing to sacrifice anything - his morals, dignity, and even other people, for the sake of his work.
His son Dievold was executed by the Cardinal for being in an anti-Balbatos group, but Nybeth did nothing to the Cardinal because it might interfere with his work. Instead, he used his dead son as one of the subjects for his unholy experiments; as a result, Dievold was resurrected as a member of the living dead - he is alive physically, but (in the original) he lacks his soul. It is also suggested that he placed the soul of his wife into his daughter Oelias.
In Chapter 1, Denam and his Order kills Moldova on their raid on Krysaro to rescue Leonar, and word gets caught quickly be Nybeth in Fort Qadriga, however, when Denam confronts him at the fortress, he doesn't express any grief for losing one of his daughters, and doesn't even mention the fact that she was his kin. Denam and Nybeth engage in battle, but Nybeth is overpowered and forced to escape.
The way his family is depicted in the game is changed, depending on which route Denam decides to go at the end of Chapter 2C. If Denam rejoins the Resistance, Oelias and Dievold will be mentioned as members of his family, whereas Cassandra, Cressida and Moldova will have different surnames and will not be mentioned as members of the Obdilord family. If Denam refuses to rejoin Leonar in his cause, Cressida, Cassandra and Moldova will retain the Obdilord surname, and Oelias and Dievold will have their names changed and their background altered.
In Chapter 3N, Nybeth is seen at Ndamsa Fortress conducting his experiments on the dead. He is revealed to have found a dead Gildas in Rhime after the Bakram invasion and used his body for Necromancy purposes. Denam arrives at the fort with Oelias and Dievold and confront him. Nybeth escapes after a fierce battle, leaving a dead (again) Gildas after the battle.
In Chapter 3C, Nybeth leaves Cassandra and Cressida behind to research on his work at Brigantys Castle, but Denam crashes his way into the Brigania Plain, killing Cassandra and Hektor Didarro, Moldova's fiancée, in the way. When Denam reaches Brigantys Castle to confront Xaebos Ronsenbach, Xaebos urges both Nybeth and Cressida to flee the castle. Cressida insists on fighting and avenging Hektor and her mother, but Xaebos is able to convince the young necromancer to flee with her father.
In Chapter 4 through the Chaos Route, Nybeth start doing experiments on dead soldiers through southern Valeria, with Denam intercepting one batch of undeads in Balmamusa. Nybeth planned to attack Almorica Castle with this, alleging that this would bring the revenge those dead souls seek. He places Dievold at Fort Qadriga just for this purpose.
Nybeth and Cressida end up arguing over this at Golyat, with Cressida in complete disbelief over her father's lack of respect for life itself. Nybeth states that his experiments grants those dead people the chance they deserve to exact revenge on the people who killed them, and Cressida disagrees. Nybeth then reveals that he used Moldova, Cassandra and Hektor for his zombifying experiments, and uses the three to ambush his own daughter, with Denam arriving just in the nick of time. Nybeth then summons his newest experiment, Vyce Bozeck, who was hung up in Heim, to repel the Hero of Golyat. Denam manages to repel both his dead friend and Nybeth and save Cressida, and Nybeth is forced to flee once again.
Later, Denam and his troops encounter him again, but this time in the Palace of the Dead. On the Neutral Route, Nybeth confronts Oelias once more and reveals to her that her soul is that of his former wife. Denam shrugs the confusion off of Oelias, who gains renewed will to fight her father. On the Chaos Route, Cressida tries to stop Nybeth with Denam's help. In Law and Chaos Routes, Nybeth is shown to have made experiments to Xaebos and Leonar for his work. After Nybeth is killed, he resurrects himself by the power of the Ring of the Dead and gains great new powers as a Lich.
Denam and Nybeth have a final confrontation at the Altar of the Beyond, the last level of the Palace of the Dead. After a fierce battle, Denam finally manages to slay Nybeth for good. Nybeth dies in disbelief that becoming a Lich hadn't made him immortal, yet he believes that by dying he finally became one with the Darkness.
Neutral Route, before Ndamsa Fortress
"A Galgastani necromancer who once served the Kingdom of Galgastan. He was consul to Almorica while it was under Galgastani control; however it appears he left his duties to a knight in his service, and was rarely seen in public.
His whereabouts since the downfall of the Kingdom of Galgastan were not known until he was discovered continuing nefarious experiments at Ndamsa Fortress."
Nybeth's name derives from the demon Nybbas, a low-level demon who notably acts regal to lure in victims and often depicted with a permanent smile.