Near impossible to hit without completing Bridge Puzzle
Impossible to be harmed by when the Bridge raises
The Bass only appear at Akropolis Tower, Bridge. It is a mutated fish NMC. If the bridge puzzle is solved (by entering 561 on the keypad next to the bridge), they are of no consequence (See the Water Bridge Puzzle for more details).
If the puzzle is not solved, Bass can deal a lot of damage to Aya (along with POISON status) as she walks through the water and they take passes at her. While not 'impossible' to attack the Bass, the extreme difficulty of aiming and attacking with a weapon in the water while being continuously hit may require a player to use a large-scale, area-of-effect PE spell like Inferno, Apobiosis or Lv.3 Plasma, to take them out.
While Aya gets credit for three kills, there are six in the water. The player only needs to kill three to win (the rest disappear).
It is possible to retreat from the water, but the player will still be in active combat mode and leaving the room will incur the usual penalty.
The Bass has two different HP values, depending on when and how Aya fights them. If the player chooses to fight them in the water, they have 1 HP. If the player raises the bridge before fighting them, they are all given 80 HP. If Aya leaves the room and comes back after raising the bridge, but not killing (all) of the Bass, they will have 1 HP again.
A curious anomaly: After raising the bridge with the Bass on them, all attacks will ignore the usual Attenuation penalties.