I find it interesting that all the vampires are women and all the familiars are men. Aside from the fan service factor, I'd wild a guess that "only women can become full vampires" and this'd be crucial later because Chika is eligible.
The second interesting thing is that the familiar's weapon is called the THIRD death, with no mentions of the first or the second, or what kind of death it is. If "death" here refers to the life cycle of vampire, then the first death is when one ceases to live as a human, and thus there must be an another step before one becomes a full vampire, which would be crucial for Chika. If it refer to the means vampires are killed, then the first death would be the sun, and the second death unknown as of now, ready to be hooked into a plot twist later.