They serve the same military purpose as siege weapons and war machines, and are used by Rubrum to counter Milites Empire's advanced weapons technology. In addition to their standard forms, Eidolons boast higher ranks and forms, giving them more destructive potential and utilization. Following the deployment of the crystal jammer, only the members of Class Zero retain the ability to summon these creatures, though they can only do so by sacrificing their life force, removing them from battle for the remainder of the mission. As such, they are best used for last resort attacks.