Along with the other elementals, Aeros can be encountered in the Amala Network and the Amala Temple, but cannot be recruited. To obtain one as a minion, the Demi-fiend must fuse the appropriate demons of the same race, or get one in exchange for gems at Rag's Jewelry in Ginza.
"A living embodiment of one of the four major elements: wind."
Or an Accomplished Aeros can be obtained through the COMP hack system
Shin Megami Tensei: Strange Journey
"This low-level wind elemental controls one of the four prime elements that compose the world. It is a fusion of "heat" and "moist" essences, forming the basis for an exponential energy increase."
—Shin Megami Tensei: Strange Journey Compendium
Devil Survivor 2
"This low-level wind elemental controls one of the four prime elements that compose the world. It is a fusion of "heat" and "moist" essences, forming the basis for an exponential energy increase."