My understanding is that Japan is not super lenient with self-defense even when you are like struggling to free yourself from a kidnapper. The reality isn't as ridiculous as some manga plot setups, but it is a very different standard over there.
Intentional killing, no matter how bad the guy was, probably means jail time. Now that said, this isn't America, so she's not looking at 50 years; honestly with the mitigating circumstances, it's probably more like 5 years.
Intentional killing, no matter how bad the guy was, probably means jail time. Now that said, this isn't America, so she's not looking at 50 years; honestly with the mitigating circumstances, it's probably more like 5 years.