So, the last Graviton Core I need is in Sunleth 400AF according to this:
Which I unlock from a gate in Yaschas 100AF?
For which I need a wild artefact.
Which I get from Yaschas 100AF?
Let's see, I have all wild artefacts (and all, used up) except the one from Yaschas 100AF, A Dying World 700AF and the casino.
Have not yet unlocked the dying world.
I heard you need to beat all missions to get the Yaschas 100AF wild artefact (according to this http://www.youtube.com/watch?v=kKO_4QUPOA0
How do I beat them?
Or rather, how the **** do I continue the main story?
Can you tell me the steps necessary to get the last graviton core?
First of all, how many Graviton Cores do you already have? You only need five (out of a potential seven) to progress with the main story, and it's sounding like you've spent enough Wild Artefacts that you probably have access to a different core besides Sunleth 400 right now. Have you checked Oerba 400 or Yaschas 110?
As for addressing the specific issue in Yaschas 100, yeah, you just have to solve all of the red sphere puzzles and teomporal distortion puzzles. The red spheres can only be done one at a time in a predetermined order, so it can be tedious, but the quests are all basically "go fetch this and bring it back" so there's nothing too complicated. The temporal rifts are puzzles like you've done in oerba 200 and possibly the other Oerba times, so you should be familiar with how those work.
You can wax my huge spoon.
First of all, how many Graviton Cores do you already have? You only need five (out of a potential seven)
Oh, I assumed I need all 7. I have 6 now.
I guess I can just continue for the time being.
The red spheres can only be done one at a time in a predetermined order, so it can be tedious, but the quests are all basically "go fetch this and bring it back" so there's nothing too complicated.
Is there a guide on it?
Actually of all the fetch quests so far I only managed to find a single capsule, so I'd rather use a guide instead of running around aimlessly.
I actually found the red orb items on my own because I'm mentally unsound like that, but you might try the fragment guide and see if it helps. It helped me scrounge up some of the other fetch quest items throughout the game.
Unfortunately, it sorts fragments by type instead of by zone/time, but it's still a handy resource. These red sphere fragments can all be found under the "Crimson Memories" sectoin, but bear in mind it may mix stuff between Yaschas 100 and Yaschas 110. You might also try some of the full FAQs and just look for the section on Yaschas Massif 100.
You can wax my huge spoon.