Are you serious or just F*&King with us?
Chi no Rondo, or Rondo of blood, is the prequel to Symphony of the Night. Dracula X Chronicles in a remake of Rondo of Blood.
So, when you start Symphony of the Night (SotN), you play the final battle from Rondo of Blood just to show you what happeded.
Alucard is Dracula's son, and is the main character in SotN