Why is it ? The idea of a Kitsune doesn't really bring and immateriality to mind.
I suggest putting the name in text of the passive skill.I suggest something like this.Tails: Generate 1 tail per turn up to 9. 1-8 Kitsune gains +1|+1. The 9th Kitsune gains Immaterial. Tail Defense.Notes: Tail Defense: Kitsune looses 1 tail per damage source.
the art is incredibly epic and I love it. the mechanic however isn't very tight and nobody would use this card to make a good deck as it relies on uncertain probabilities etc. Make the mechanic something more solid and useful for pvp style decks and keep the art.