Kaguya as the rabbit goddess

[MAN OF SIN]

Hagoromo stated that Kaguya was stronger than anyone. That would include the Juubi he fought. So Kaguya had to be nerfed at that point in time.

 

[Angelic.]

where was it said they fought kaguya? we dont know how she ended up in the shinju yet

 

[Seventh Sama]

A lot of the 9 tailed beasts took on characteristics of Hagoromo (like the Hachibi's beard). Maybe this Juubi is only taking on characteristics of Kaguya (the Rabbit Goddess) because she is the one currently with its chakra. If Obito's history of the tailed beasts is anything to go by then Hagoromo also lost control of this chakra shortly before he died. Maybe Hagoromo's Juubi would have looked different if he hadn't stopped the process mid-way by splitting and releasing the Bijuu.

Losing control

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Well, Kaguya is the juubi per say but yeah I agree with what you're saying.