In Akainu's and Aokiji's case their devil fruit abilities neither negate nor disable each others properties.
Whether Akainu hits Aokiji with a magma fist or Aokiji hits Akainu with an Ice Spear, without haki it won't hit their actual bodies since neither Magma nor Ice negate/disable the properties of their respective elements.
It's no different to a bullet or a sword going through them.
Whether Akainu hits Aokiji with a magma fist or Aokiji hits Akainu with an Ice Spear, without haki it won't hit their actual bodies since neither Magma nor Ice negate/disable the properties of their respective elements.
It's no different to a bullet or a sword going through them.