About as straightforward as the previous. Note, there is no real reason to do this on any harder difficulty than Normal, unless you find a Client Order that specifically says to on Hard or above.

 

Kill the enemies in the starting area until they stop spawning, then travel to the four corners and kill any enemies that spawn there. Keep going in circles to dispatch enemies until Henrietta speaks. When Henrietta shows up and says certain things, certain enemies spawn in specific corners. The list is as follows:

北東の島付近にて大型のダーカー反応を感知。 (Wolgahda has spawned in the TOP RIGHT corner)
南東の島付近にて大型のダーカー反応を感知。 (Decol Melluda has spawned in the BOTTOM RIGHT corner)
中央の島付近にて大型のダーカー反応を感知。 (Zeshrayda has spawned the CENTER area)

After killing the last boss, proceed to the next area.

 

Welcome to the Seabed. In this next part, kill the enemies while also looking for switches that aren't protected by barriers. Hit them all and kill all the enemies to lower the barrier.

 

Next, hit all the Red and Blue switches, while also killing the enemies. If you reach a switch that isn't on yet, it means an enemy on the other side is still alive. Ex, a red switch isn't on, so an enemy on the blue side is still alive.

Once everything is dead and all red and blue switches pressed, go into the final area. Press and hold all 4 of the switches, kill the enmies that spawn from them, and then you're done.