Commonly, an aberration means an absurdity, an error particularly contrary to common sense. An aberration is often subject to discrimination and causes fear and hatred by others.

These are the criteria (plus the fact that he is of surreal and / or supernatural origin) that matters most to define someone as an abberation.

It depends on the context and history of the VN too. In our present time, a human clone is considered an aberration but in a futuristic world it could be seen as a normality.

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The reason for rejection is already within the description - "it depends on the context". The term is so subjective, there is no viable way to make it a trait.