After the tragedy that killed his mom (Ai), he changed. -- becoming cold, calculated, cunning, and discreet, he would do anything to find the man who killed his mom. A man is willing to do whatever means necessary to see his goals through. The pain he underwent tends to resurface anytime he seems to forget his goals. This is the case when Kana Arima suggested that he'd look back at his happy memories in Chapter 50 to improve his acting on the spot. It is a case of Post-Traumatic Stress Disorder 