In مِنْ أَيَّامٍ أُخَرَ, both «أَيَّامٍ» and «أُخَرَ» are genitive, but one is marked with kasra and the other with fatḥa.
The same is true in بِرَجُلٍ أَسْوَدَ.
Rule: an adjective follows the syntactic case of its noun, but the visible case marker need not be identical when the two words belong to different declension classes.
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Causes of Diptote Status — ʿAdl and Waṣf
In مِنْ أَيَّامٍ أُخَرَ, both «أَيَّامٍ» and «أُخَرَ» are genitive, but one is marked with kasra and the other with fatḥa.
The same is true in بِرَجُلٍ أَسْوَدَ.
Rule: an adjective follows the syntactic case of its noun, but the visible case marker need not be identical when the two words belong to different declension classes.