I'm trying to recall any time in the story where haki is described as something quantifiable that can "run out", and only Luffy is coming to mind. Now, on its head this comes across as sheer convenience so his fights can be dragged out to inflate some tension, giving him the underdog status in fights even though it doesn't really make sense at this point.
I partly ask this because characters who have CoC don't seem to use it when it would be ridiculously useful. If haki is a pool of magic that needs to be conserved and used carefully in fights, that'd be acceptable, but it's *never* talked about that way outside of Luffy.
My Marvel No-Prize is that the Nika fruit has an adverse effect on the user's haki, making it a consumable resource the more that the user approaches awakening.
I partly ask this because characters who have CoC don't seem to use it when it would be ridiculously useful. If haki is a pool of magic that needs to be conserved and used carefully in fights, that'd be acceptable, but it's *never* talked about that way outside of Luffy.
My Marvel No-Prize is that the Nika fruit has an adverse effect on the user's haki, making it a consumable resource the more that the user approaches awakening.