The Resonant are Garlean supersoldiers in Final Fantasy XIV imbued with a powerful artificial version of the Echo (Elidibus considered the Resonant a "borrowed Echo".). They can manipulate the power of the aether to detect minor changes in it to predict and avoid incoming attacks. The Resonant project was developed by the Garlean scientist Aulus mal Asina to overcome his people's natural inability to use magic.
Though the Garleans are intellectually and physiologically superior in almost all aspects, they lack the hereditary traits required to manipulate aether, thus making it impossible for them to use magicks. They thus suffered decades of oppression by other races, and were driven to seek shelter in the cold northern region of Ilsabard. The region's vast deposits of ceruleum led Garleans into developing magitek: a revolutionary technology conceived to compensate for their disadvantage.
Though magitek made Garlemald a world power, Aulus mal Asina saw it as a temporary solution to an intrinsic problem, which he believed could he solved by manipulating the Garlean genomes. Aulus began his research with funding by Zenos yae Galvus, who went through the perfected process after using the Ala Mhigan Fordola rem Lupis to test the experiment. The resulting transformation enables Zenos to merge into primals and control them, and to cheat death like an Ascian.
By the time Zenos retrieves his body from Elidibus, he has gained mastery over his Resonant abilities, such as being able to project magical barriers and teleport, becoming an Ascian in all but name.