After reading an interesting post on the "anti-midian" meaning of Seras' battle rifle/cannon thing, I would like to know what the motif of Vladimir Harkonnen from the "Dune" series has to do with her cannon?
Let me give you an example:
Alucard's awesome pistol "The Jackal" symbolizes Walter's future betrayal of Alucard because, in the Fred Forsyth book "The Day of The Jackal", the character The Jackal kills everyone who helped him make his forged documents and weapon as a way of covering his tracks as he tries to kill Charles De Gaulle. In the dream sequence where this motif is introduced, The Jackal comments, "Never trust the man who makes your own weapon," which foreshadows Walter's betrayal.
So since Seras has two huge cannons that bear the Vladimir Harkonnen name and she even talks to Harkonnen in a trippy dream sequence, what kind of symbolism or motif does Harkonnen have in relation to the Hellsing universe?