He was there to show some team power among the Fallen 13, as most of them intend to work individually. In the original setting Luo is supposed to be a guy with shocking eye vision, as well as a surprisingly strong close combat skill set, thus making him a great partner for Jing. Unfortunately that would drag the timeline longer than I could afford. Luo Sun’s adventure had to be cut short .
My main goal when designing him was to portray a real air of arrogance about him. They were many designs before going with the current incarnation. I originally had a much gruffer appearance laid out before deciding to make him a younger, prettier accomplice to his sniping companion. There was a bit of back and forth deciding the design for the pupils of his eyes before finally going with the current design.