WARNING: The following contains spoilers for Castlevania Season 4, available now on Netflix.
Netflix's animated adaptation of Castlevania began by drawing direct influence from the 1989 video game Castlevania III: Dracula's Curse, before going on to weave in characters and elements from the 2005 game Castlevania: Curse of Darkness. The most notable inclusion from Curse of Darkness into the animated series was Devil Forgemasters Hector and Isaac, who began creating monsters for Dracula's armies before falling on opposing sides in the power struggle left by the vampire lord's demise.
Hector and Isaac are finally reunited in Castlevania's fourth season, however, the two friends' have a far different chance to catch up than they did in Curse of Darkness.
Disillusioned with humanity and vampires alike, Isaac cut a bloody path around the world over the course of the anime, all while steadily harvesting the bodies of his victims to craft his own roving army of monsters. Eventually, Isaac began to show signs of his old links to humanity, instructing his army to bury the dead that couldn't be transformed into monsters and rebuild devastated cities for potential future civilizations to settle in them in Season 4.
After deeming his army strong enough, and learning of the vampire lord Carmilla's plan to subjugate humanity and rule the world, Isaac turned his army back to Europe, triggering an epic showdown, while an imprisoned Hector continued building monsters for Carmilla's own army.
As Isaac and his army battle through Carmilla's horde of monsters and vampires, Hector greets his old friend in the heart of Carmilla's castle. Rather than the two Devil Forgemasters coming to blows, Hector cuts off his own finger bearing the magical ring that forces him to obey Lenore's every wish. Now free of the vampire sisterhood's control, Hector gives Isaac the means to confront Carmilla directly and overthrow her rule, with Isaac visibly appreciating his old friend's help.
This differs significantly from Curse of the Darkness, wherein Hector and Isaac were at odds for the entire game's story. Three years after the events of Dracula's Curse, Isaac manipulates an angry mob into burning Hector's fianceé Rosaly at the stake, who is under accusations of witchcraft. Vowing to avenge his love, Hector pursues Isaac back to Dracula's castle and battles him to the death. Upon defeating Isaac, Hector discovers that this vendetta was all the grand plan of Death, who intended to resurrect Dracula in Hector's body. The ritual was forced to use Isaac's body instead, causing an imperfect resurrection and leading to Death's eventual defeat at Hector's hands.
Rather than being committed as mortal enemies, the animated series' iterations of Hector and Isaac's friendship is maintained -- even as they wind up on opposing sides of an epic war. Whereas Curse of Darkness was a thematic meditation on the cost of vengeance, Castlevania Season 4 shows the value of keeping sight of one's humanity and the relationships that define what it is to be human. Hector and Isaac's friendship is a prime example of this. Hector doesn't get quite the happy ending he experienced by the end of Curse of Darkness but still emerges with his greatest friendship intact.
Castlevania stars Richard Armitage as Trevor Belmont, Alejandra Reynoso as Sypha Belnades, James Callis as Alucard, Theo James as Hector, Adetokumboh M'Cormack as Isaac, Jaime Murray as Carmilla, Jessica Brown Findlay as Lenore, Bill Nighy as St. Germain, Jason Isaacs as The Judge and Rila Fukushima as Sumi. All four seasons are available to stream now on Netflix.