Tsu's main mode is a tower where Arle Nadja selects opponents to battle via roulette. Each "floor" of the tower has an EXP total that the player must reach in order to advance. If the player defeats all of a floor's opponents without meeting the goal, one final opponent will appear. If, after defeating this extra opponent, the player still fails to meet the goal, Arle is booted from the tower and the game ends.