I'm a big fan of the Castlevania games and the more I play those and Melty Blood, the more similarities I see between them. I'll begin....
Richter Belmont: Wields a whip. Family had studied the art of alchemy in the past. Served under the Church's command earlier on.
Sion Eltnam Atlasia: Alchemist. Wields a whip-like weapon. Worked for the Church prior to the events of Melty Blood.
Dracula and Warakia: Vampires. Costumes are similar, most noticeably the colors.
Sidenote: Warakiya is the name of the town that fell under attack at the start of CV3.
The throne and wine glass.
Arc Brunestud and Maria Renard: The stunningly beautiful blondes.
Richter Belmont: Thousand Daggers (knife item crash)
Ciel: EX Knives
Sister Tera and Ciel(color #13): Nuns. Identical colors.
So those are the similarities I've noticed so far. If there's any others I might have missed, just mention them.