I was watching the GS Mikami movie (again) just now. Aside from realizing I'm growing out of my anime phase, I also noticed some similarities between the movie and Castlevania.
First off, the character Meiko slightly resembles Maria from RoB, I think. Granted, Meiko uses shikigami while Maria uses more natural elements (if you can call a dragon natural), but they are somewhat similar. Both are kinda cute. Both are kinda annoying. Both have an entourage of helpers.
http://anime.mx/wp-content/uploads/2012/08/1161363020_f1-300x223.jpgThe second thing was Nosferatu in GS Mikami was "driven out of Europe by the Vatican" and took up residence in Japan. He replaced Oda Nobunaga, which is not really a unique plot in anime (he was demonized in Samurai Deeper Kyo). The thing is, the most powerful vampire in Europe is resurrected in Japan.
In the GS Mikami movie, Nobunaga's vassal Mori Ranmaru is an albino [spider] in white clothes. In AoS, Soma has white/silver hair and a white overcoat.
GS Mikami came out a couple years before Rondo.
GS Mikami the movie came out many years before Aria.
Just something that popped into my mind while watching.
Oh, and one of the composers for CV1 was the composer for the GS Mikami game on the SNES.