I believe that the anime answered this for us. I seem to recall her Vice-Captain saying something about her Shikai, just after Minazuki spewed out all of the victims from Ichigos' strike against the Vice-Captains... I seem to recall that Isane was injured, but said something about it, just after it happened. Though, my recollection is hazy, so I could be wrong. XD

It's considered to be her shikai, but aside from the release command being unknown, it really just seems like a manifestation in every shape and form, aside from the fact that her entire sword morphs into the manta ray-like creature. If it IS her shikai, though, then I have to ask how it's different than actual manifestation? Granted, we haven't really seen it in action. Just one time when she was transporting the lieutenants and a second glimpse from her regei during the Invading Army arc.

Well, we do see her Manifestation in the Rogue Zanpakuto Arc, so maybe it is truly her Shikai. Her Manifestation was the girl with the eyepatch, who looked kinda evil, considering that her Zanpakuto is meant to be about healing lol.

really can't choose, I just know that i hope that it isn't and that her shikai is stronger than that.

Her Shikai isn't meant to be 'strong', it is a healing Zanpakuto. Now that I think about it, it must be her Shikai, because it certainly can't be her Manifestation form, since we've already seen that. I'll make my pick now.

Fair point there, BP. We have already seen the manifestation, though it was a filler arc. But that's all the more disappointing. One of the oldest captains' shikai is just an alternate manifestation form. Very disappointing.

Honestly can't tell at all.

if this is her shikai, i wonder what her bankai is.

@Exorcist, but we haven't seen her abilities in Shikai yet... for all we know, Minazuki could have a couple of epic abilities. Plus, even if her Zanpakuto is more about healing, Unohana has an impressive cache of Kido spells she can use and she could simply fight using her sealed Zanpakuto. And then there is the question of her Bankai, which I also wonder what it might be.

@Blackpanther666 you said that the manifested form of Minazuki during the rebellion arc was the one with the eye-patch on a earlier comment, but actually the one with the eye patch is one Kyoraku's Zanpakuto Katen Kyokotsu, Minazuki was the one with the hood.

Minazuki (spirit)
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Katen Kyokotsu
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