N'Doul is blind and navigates using a cane, which he's genuinely skilled with—he came close to killing a fly with it, which says something about his precision. He operates by what looks like a genuine warrior's code. Jotaro figures he would've probably sided with them if they'd caught him before Dio did, suggesting N'Doul had some integrity beneath the loyalty. After his defeat, he actually turns his own Stand on himself to make sure he won't accidentally leak any of Dio's secrets to the group. That's the kind of commitment he brought to his work.
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