He Deceived Everyone By Pretending To Be Weak But He's Actually A Monster

On an alternate reality Earth overrun with mutated nano-machine-beasts called Filth Monsters (Contaminoids in Funimation's translation), humanity is forced to live in large mobile cities called Regios and learn to use weapons called DITE (pronounced Di-Te) and harnessing the power of Kei to defend themselves.
Anime Name: Chrome Shelled Regios