The pureblood are immortal. Yet for some reason, so few of the families exist anymore. There are only nine clans left, and within them only a precious few.
[Because for so many, after living for an eternity they grow wary of life and seek death. To Yuuki... that kind of thing is much too sad.]
But also because we linger on for eternity unless specially killed, no one else is able to match our life spans.