Correct me if I'm wrong but, that's not how self-defense laws work right? I've only done the basic google search and I have no clue if I'm right or not but in japan, you have to prove that your actions were justified. And there were plenty of witnesses and a victim with a massive injury in his back possibly leaving him crippled. In the end, I'm not an expert at all and all I did was a 5-minute google search so if you know if got any of this wrong let me know, I feel it is very important to get something like this right, and if a story changes a law for the convenience of the plot, there should be a disclaimer of what it's changing. Who knows, I may just be rambling all the wrong information.