Apothisexual is known as a micro-label. Meaning that by saying that one is apothisexual it is implied that one is also asexual. In this case asexual is the primary sexual identity and apothisexual acts as a modifier, making a specific sub-category of asexuals.
The romantic counterpart to apothisexual is apothiromantic.
The prefix apothi- comes from the Greek word apothisan, meaning repulsed.