Though not much is known about Miyuki she tends to disappear for long periods of time and then reappear somehow having gained a significant boost in her life expectancy, most likely due to either trips to the outside world or uses an immortal time travel as a tool to explore+
The multiverse for new prey, as a very special fox youkai she needs to drain the life force of other living beings to survive she does so through her concerts which allows her to mass drain from all those who attend she has been known to leave her victims alive too