The H.A. Troopers are the footsoldiers of the Human Alliance. They are the ones sent out into the field to hunt down Devil Beasts as support to Devilmen associated with the HA in order to either imprison or execute them. Unfortunately, as they are still human, they are usually just seen in the background.
The troopers are armed with weapons and equipment to hunt down Devil Beasts that have appeared in Japan. Many of them are usually given supporting roles such as giving distractions that Devilmen can exploit in targets. They also handle situations where civilians might be involved including schools.