Trauma Center - Under The Knife

Unlock Bonus X missions in Challenge mode:
Finish the game. Completing each X mission unlocks the next mission in the
series, in the following order:

Kyriaki - X1
Deftera - X2
Triti - X3
Tetarti - X4
Pempti - X5
Parakevi - X6
Savato - X7,