I need Kotarou to walk away from his defeated attacker while saying something like "Compared to Tae, your strength is... lacking." It's as cheesy as it gets, but you need that once in a while.
Damn, I wouldn't blame him not wanting to go back, either, if that was how he was raised. If he had to go for any reason, it would probably to finish the job Death has set.
The trauma even for a ninja. It is the memory of being a child and your own father who you would trust implicitly at that age suddenly trying to kill you. Again showing that getting help with mental issues is important. Mental health is health and should have no stigma to getting treatment.