Naoki definitely has dealt with a lot of crap since becoming a demon, so maybe he can help? There is plenty of angst to dig up if convinced to open up or if he thinks it can help; watched his teacher and the world die, demons killing each other, his friend having lost an arm and then turn into a demon, the slaughter of human-like demons, killing his own friends when they turned against him, etc. That last one he still hasn't revealed to others btw.