Back with Lightning, this area is now filled with Cie'th as well. In a dead end to the left is a Power Wristband which will give a strength boost. This should be equipped on Lightning to make her strength stat quite high at this stage. You should also make sure Sazh has an Iron Bangle.
Return back to where you were and run up several flights of steps, fighting the Ghouls in your way as you go. At the top, you may notice a different type of Cie'th blocking a doorway. This is a Ghast and it is considerably stronger than the Ghouls you've been fighting thus far. With Lightning's strength however, it shouldn't pose too much of a problem, though you may need a Potion just to be certain of victory. Save if you wish then move to the next place.
A gauntlet of Cie'th stand in your way, with the final group being two Ghasts. Dispose of them like normal but don't be afraid of healing because you will likely need to a couple of times. Move to the marker for another heart-wrenching scene.