Okay. I am personally leaning toward tier 0, but it is best if we get some input from @Ultima_Reality .
Yeah, so, I figure I have to lay down some foundations to explain where The Creator being Tier 0 would come from, in this case.
So, basically, "Featherine" as the personal, active entity which appears in Umineko actually has, just like the Voyager Witches, a true self which exists separately from her physical form as an abstract law which influences the whole setting. Piece describes Featherine as personifying the pillar which sustains the world in Saku, for instance:
私は、尊厳なる観劇と戯曲と傍観の魔女であらせられる、大アウローラ卿よりカケラを預かる使者として生み出されました。 大アウローラ卿が、世界を支える柱という偉大なる蝋燭に灯る炎であるならば、私はこの程度の蝋燭なれど、大アウローラ卿の炎より火を分けられた、分祀されし存在なのでピス。
I was created by none other than the great Lady Aurora, the Grand Witch of Spectating, Drama and Theatergoing, as her emissary. If the great Lady Aurora is the greatly lit candle, the so called pillar that supports the world, then this one is a candle of such degree, however, the flames of the great Lady Aurora is an entirely separate flame.
This fundamental nature is something that we know must exist independently from Featherine's personal form, given how the novel notes that she constantly dies and resurrects herself because of boredom, with that having no effects in the universe at large. Further than this,
it's also stated that her human form isn't actually her real self, and that it's just a shape she assumes to present herself to others.
This isn't just a demonstration of Shapeshifting because Witches as a whole are also stated to be fundamentally human on a mental level, hence why they default to human appearances, and become "scraps of seaweed" in the depths of oblivion if they choose to abandon those forms, basically the closest thing the higher domains have to death. So Featherine's form being pretty much an artifice to her definitely points to something else being at play.
So, finally, we also have
this exchange, where "Featherine" switching back and forth between her human and witch identities is compared to how an actor can assume the roles of several different characters if they want to, with Ange even putting emphasis on how both "Tohya Hachijo" in the Human World and "Featherine Augustus Aurora" in the higher worlds are just temporary identities being assumed by something else, hence the difference between the higher and lower planes is trivial to her, and going from one to the other is "just like having a slightly different background behind the stage."
All of this is referenced pretty often by Ryukishi in several interviews, where he explains that his characters have so many expies throughout several different works because they are being played by the same "Actor."
This is a series of interviews of Ryukishi07 and Witch Hunt conducted at the French anime convention Epitanime on May 26 and 27, 2012. The first interview concerns what Ryukishi did before making When They Cry, his thoughts on the franchise becoming as popular as it is, and his new work Rose...
07th-expansion.fandom.com
21/ In Rose Guns Days, there is a character that has a striking resemblance to Battler, even the name is similar, is it the same person?
He likes to have old characters appear in newer works. He answered that you need to think of the characters in his works as actors of a movie. Now that Umineko is over, the actor playing Battler is now playing another role.
So, TL;DR: Featherine's true nature is an abstract force which sustains the whole setting while existing beyond the three domains, and perceiving the difference between them as being meaningless, as "Featherine Augustus Aurora" herself is also just a temporary identity being played by this force. Given how her being
1-A+ seems to be something nobody has any issue with, then that fundamental entity would be
High 1-A, in my view.
Now, the issue is that we don't ******* know where exactly Featherine's "actor" is placed in the cosmology, or how it relates to The Creator, especially given how vague both of them are, hence why I am neutral on whether or not the latter can be Tier 0 based on scaling from the former, like people said above.
