For the Harrower prestige class the alignment requirement is:
Alignment: Must be chaotic, evil, good, or lawful (cannot be true neutral). Most harrowers represent alignment extremes: lawful good, chaotic good, lawful evil, or chaotic evil.
In our campaign, we're playing with a five-by-five alignment system (image below) and so that leads me to wonder, would the ruling be that the requirement for a Harrower is to be both chaotic, evil, good, or lawful and cannot be true neutral, or that the requirement is to be an alignment that is not true neutral?
Five-by-five alignment chart (ft. Avatar: The Last Airbender).