You need to visit the crash site on Zeffo. When you reach the large debris, look to the left. There will be a monster. Kill enemy, go up and turn off the energy barrier using the ability of BD-1.
So you will find yourself in the bowels of a fighter, where you will need to solve a number of puzzles. One of the main mysteries is the hall with a pool and electricity. Before turning on the power, cross to the other side and cut the thick cable to the right.