The Los Angeles Arc is the fourth story arc of Souyaku Toaru Majutsu no Index, covered in Souyaku Toaru Majutsu no Index Volume 4.[1]
Following the crippling events of Christmas Day, Academy City and the Anglican Church have joined forces for a counterattack against R&C Occultics, but their enemy responds by causing the entire population of Los Angeles to disappear. Travelling to the empty and frigid city with Index, Stiyl Magnus and Kanzaki Kaori, Kamijou Touma finds himself fighting for the sake of a mother and daughter caught up in it all, while back in Academy City, Accelerator goes ahead with his trial.[1]