I do forget from time to time that the fairies are probably older than most of the cast. 🤔 But, well... since they are fairies, maybe that only, and only translates to "They were there at that time" ?

Hmm... but Eiki talks to Cirno in PoFV as if she has to not only judge her, but eventually send her to that afterlife. So they do die, somehow – just as somehow they are born.