Season 1 and 2 are basically a single season. The first 4 episodes are literally all set up and building to the "second" season.
That said if we want to go this route then Season 1 and 2 are based on Castlevania 3.
Then the final season is of course Alucard taking it head on to Shaft and Dracula in Symphony of the Night
That said if we want to go this route then Season 1 and 2 are based on Castlevania 3.
Season 3 is based on Castlevania 1 which chronologically comes after the story in season 1 and 2 and features Simon Belmont, aka Conan the Vampire Hunter.
A potential Season 4 would could then cover Castlevania 2 which is a direct sequel to Castlevania 1 and about Simon recovering the scattered organs of Dracula to resurrect him... before killing him again.
Season 4 could also just skip to the famous Rondo of Blood where Richter Belmont and his allies take on Dracula.
Then the final season is of course Alucard taking it head on to Shaft and Dracula in Symphony of the Night