Gekimuzu Difficulty
     To  obtain a 4th difficulty, you need to get the highscore on all
4 modes of gameplay.

Zoo keeper: 1200000+ points needed.

Tokoton 100: 1800000+ points needed.

Quest mode: 10000+ Yen needed.

Time attack: 600000+ points needed.

     After  getting all 4 high scores, a 4th difficulty appears in the
top line of the option menu.

     This  difficulty  means  "Expert" or literally "difficult-player"
and  has  a  huge  advantage  of  doubling  all  the normal points you
achieve. This secret was found by mtpfreak and verified by bemani.


Expert difficulty:
     Record  the  top score in Zoo Keeper, Tokoton 100, Quest and Time
Attack modes.