Underdog Knight (2008)

Lao san is a highly motivated navy man. In saving a friend from drowning he suffers hypoxia. The lack of oxygen causes permanent brain damage and he is no longer able to function to a normal level of intelligence. After being discharged from the navy he remains caught obsessively in the training he received. With only a young deaf boy for a friend he moves around the city fighting crime and trying to teach petty thieves the simple lessons of right and wrong using his martial arts background.