I found it hard to determine the boundary of OOCness.

When non-human creatures or objects, like Pokemon or even inanimate items like rings are being turned into human beings, whether they are in the real human society or not, surely their personality would change under the setting of the AU.

Is it acceptable as long as the author justified it well enough?

For example, let's say if all Redwall characters were humans living in fourteen-century England under an AU setting. Some of their minor characteristics would definitely change because they already had different backstories and experiences to begin with, but it still portrayed most of the canon personalities well enough.

Or for hateful characters that loathe human race simply because in canon, they were much higher beings than humans and viewed them as pests.

If such characters were to be put into a Humanization AU where they are human beings, it did not make sense for them to have the same kind of hatred as they are humans themselves. Generally they will still be hateful and display great animosity towards everyone around them, but they would not possibly despise their own species.

So......if such an AU make sense, even if the background and minor trait of the characters are changed, do they really qualify as a badfic?