From the SMT wiki:A commonality between characters of the Strength Arcana is their strength of heart. Strength characters are not upset easily and typically portray the fortitude that the Strength card represents in readings.

Basically, Noboru hides all his emotions and shields himself from all kinds of bad things that happens to him. But even the most hardened shields can be broken. Which is why I keep repeating that while they may not hate him, Rui and Sachiko may severely dislike Noboru after his dungeon.