It couldn't be stoneskin because it's an Earth Elemental spell that targets enemies.
Rasp= DEX Down
Therefore one must conclude the 'Accuracy Down' debuff is Earth based. So there's a pretty high chance it'll be an 'Accuracy Down' Ninjutsu, which should replace Kurayami. Since Kurayami is -30, then this new Ninjutsu must be super strong, perhaps an Earth Based Flash(would be ideal since NIN already have a Blind ninjutsu).
1)Flash(Mega accuracy down for a short period of time+high enmity)**Most likely
2)A more potent Kurayami(kind of redundant...because they could always just make Kurayami San, also Blind=Accuracy down, there's no other penalty that Blind provides as far as I know. Unless Blind= Accuracy/R.Acc down and Acc Down applies only to melee. I can't think of any other reason why there are two different statuses for the same effect.
One to be born
from a dragon
hoisting the light
and the dark
up in the sky
to the still land.
Veiling the moon with the light of eternity
it brings another promise to mother Earth
with a bounty and mercy.