I explained how youkais are born from the fears inside a human's heart

Today we have traces of youkais in books and old stories

In short, youkais leave a trace of their existance to be remembered

That's why even after the body of the person dies...

As long as some humans remembers them they will come back to life

This is the meaning behind the youkais not dying

However

Komeiji Koishi

I don't think it's your case