And the Succubus because Dracula has always been portrayed as a seductive figure, and vampires in general are very sexual creatures.
yes dracula's a handsome boy but obviously more important aspect of succubus characteristics are obviously more important
and also just so it's completely clear as to why this shit's important
but here it seems completely arbitrary. As far as I know, it isn't explained in the game.
those three souls as I mentioned are
Big D's Big Three™aria explains the whole "claiming the throne" rule and that theoretically anyone can do it but someone stronger can always usurp it
combine the "claim the throne, become master" rule with
Big D's Big Three™ and
hey look it's the literal reincarnation of dracula's soul and what do you get
literally dracula (in spirit at least) with
Big D's Big Three™ claiming the throne and as a result going from "spirit of
Big D in a rando kid's body" to "oh hey you have
Big D's soul and
Big D's Big Three™ and have claimed the throne of
Big D's monster castle guess what bitches it's morphin' time only this time you get to keep your clothes and don't change into an obnoxiously bright-colored onesie"
why does this shit matter?
well something something plot progression something something "place which only you, dracula, can go" something something finish the 1999 job and cut chaos off at the source since nobody but dracula and the baddest old man on the planet can go through the door to get to chaos in the first place something something
so there ya go
it's not arbitrary at all really