This works more as a permanent, not a spell. And again, could you explain your rather specific thematics? I am seeing no correlation between foxes and healing.
As for the card, what if only one creature reaches full HP? Do the rest of your creatures all lose the healing?
it is a spell that affects all your creatures and your player,
new creatures that comes after Kitsune Regeneration is not affected by Kitsune Regeneration.
Kitsune Regeneration is attached to each creature individually like poison,
one creature loses Kitsune Regeneration does not affects another individual.
no answer for thematics.
story:
Kitsune is a popular mythic creature/deity in asia,
in stories and legends,
some people pray it to protect them,
some people pray to it not to destroy their houses,
some people treat it as evil spirits that seduces their husbands.
Kitsune have magical abilities like healing, summoning rain,
the evil nine tails can cast disaster on villages.
Most kitsunes can turn into a beautiful woman to mingle with the humans.