P10F: Academia AF400
Final Fantasy XIII-2 Walkthrough and Guide
by CMBF 
P10F: Academia AF400
Now it is time to head back here and finish the remaining items in the zone that we did not end up doing because we departed for the Tower before getting around to it. So upon arrival hit the Map NPC to turn in any of the zones you have uncovered the map for 100% to collect the Fragments for that, and then retrace your steps all the way to the Chocolina near where we battled Zenobia.
Cleaning up some odds and ends in Academia AF400
On the way grab the Kaiser Knuckles from the Treasure Sphere you need to jump up to get just before you turn to go onto the broken bridge, and then cross and battle your way along until you reach the path that is below the Chocolina -- she is at the top of the upper ramp where the two ramps are right next to each other -- head down and near the control panel we used earlier to turn the ramp we just had to hop down to the up direction is a hidden Treasure Sphere with Phoenix Blood in it to grab...
Now head back up and then up again until you are standing beside the Chocolina and look at the red ramp directly to the north right here... Jump down this ramp (it is going in the wrong direction) to the bottom, where you will find a small landing -- use Mooglehunt and you will reveal a hidden Treasure Sphere that contains the Graviton Core Delta Fragment. Well done!
Now that you have that head back up and save your game. Take a look at the map -- are there any areas we can clear on it? If not then we are done here for now!
Return to the Historia Crux now, and select the Gate for Academia AF4XX.
one thing that may be handy to inform people of in this area is that the chocolina moves depending on what area you are in...i realize this is a walkthrough so i am sure there are people following this guide like an instruction manual, but there are people like me who use it as a backup in case we get stuck finding something or achieving something. she doesn't change in every map; however, in the AF400 map, she has 3 locations. on the west side of the "bridge" to the Academy. Near the topographic researcher near the middle, and on the east side of the map on a balcony. After thoroughly scouring the map in the second and third locations, i moved on figuring i would come back to it. i had been back and forth so many times i didn't realize she was moving until i went off to explore the far side of the map some more. and that is where i found the graviton core right where you said it would be.