Kirin is a young mechanic taken in by Ellie's family (Angel Ops-- the ones who took gauge in after he was hit by the train) after his family was attacked, and his parents murdered by RUBICON for dismantling and reprograming Watchmen and Gestapo robotic units. Kirin was injured, as you probably can tell from the headgear holding his face together. It's permanent, put there by Auturo (Ellie's cousin who is a doctor) because of a badly broken jaw. Kirin cannot talk, but it is more than obvious he has a crush on Ellie's younger cousin Gidgette.
Kirin also plays a huge part in the story, as he is able to program and rebuild Watchmen mobile units and Sentinelsfor the benefit of the Revolutionists. It is his ability to manipulate and recreate lost technology that fuels Angel-Ops its rise to power against the evil empire of RUBICON.