Need help finding an Asian film I saw in the mif 2000s.

I need help finding the name of a movie. It's an Asian film, where two guys fall in love with the same woman. One of the characters is named o. The other guy teaches her how to shoot a sniper rifle. Eventually they both fight to the death for her. They make metal slug references. It ends in a plot twist where it is presumed dead. But actually fireworks go off, and the guy has an epileptic seizure and it kills him with an Uzi. They also have a train scene where he gets an epileptic seizure.