(Source:
Megami Tensei Wiki)

Ryuuji is known as a disruptive "problem student" at school whose bad behavior causes all sorts of trouble for the teachers. His rebellious, mischievous and disobedient nature are the perfect qualities to be a Phantom Thief. He is a bit short-tempered, easily taking offense from even the slightest of comments from others and can sometimes even resort to violence.