This one is story-related and cannot be missed.
After the battle with Victor it is time to ascend the tower. This takes place on 5 floors with challenging platforming sections varied with battling sections. Fortunately, every floor level has a fast-travel point.
Every floor increases the required level of the CoreBots and Joule's weapon (max level 28) and needed prismatic cores. The battles are a great way to increase the level of the CoreBots and your weapon. Some of the platforming sections may be deemed impossible during the first tries, they are doable, just keep practicing.
The final boss is a tough one, changes colors often and spaws lot of bigger enemies and shifts in shapes of all known enemies. Keep shooting with the corresponding colors, use charged shots and let your corebot attack him as much as possible (which makes it possible to beat him with an instant extract while he is distracted). When done the cut-scenes follows and the achievement unlocks.
For the battles I've put Duncan in the SP-DR-frame and Mack in the FL1-R-frame