Board Thread:Questions and Answers/@comment-26232072-20150330025950/@comment-6697950-20150330073125

"Totaly skill-based. Player skill is rewarded, PK-ing is encouraged. You don't have a 'level'. You can only power up skills through use, and your HP barely increases as you play through the game. Battle depends on the player's actual athletic ability."

Basically, hardcore because the game mostly on the player's own abilities, rather than stats, levels etc. Of course, hardcore as in hardcore for a game. Not death game kind of hardcore.