With japan weird murder/psycho cases usually with tonnes of tortures, pretty dumb to take the job. Maybe he is trying to find actual pain to finally kill himself.
When faced with overwhelming despair, every other choice besides enduring it becomes more acceptable
We don't want to die, but such people also cannot bear to cause suffering due to their own death. They know suffering, the taste of pain and despair forced down your throat. And they don't want anyone innocent to suffer such fate
It's so bad that pointing a knife to your throat doesn't bring fear, but relief
Relief that at the very least, you have this option. You have one last control over your life. That it's you, and not the pain, that will end yourself.
Of course, it is the pain causing that to happen. But people in pain aren't at the best mindset to realize that, sadly