AAPS' are droids designed by the AMA, as a means of creating soldiers that could fight and protect without risking life and limb by using small elemental spirits as living batteries for the armors.

These armors are designed to be modular and fit the needs of the city, such as fire and rescue, and of course military service, they can also be modified by the spirits themselves to personalize them. After all, spirits are people without bodies, after all, they have a choice on how they look and act, as long as they obey the magical contract.

This great reference was done by   shiblue7 who does scifi style character adopts, and commissions of course.