Star Ocean: First Departure

Finish them using them

Like Star Ocean: The Second Story, having them help each other out in battle also helps. So if Ilia ever gets KO'ed, switch to Ronyx and have him resurrect her, and likewise have Ilia throw Ronyx a couple of MP restoring items now and then. You know you are on the right track when they start thanking each other for the help.

Make sure that you do the PAs described by syaugust above as well, because that is the main push. This just helps to smooth it over.

what syaugust8 says is true, but also, they must have a high AR when you are ending the game.

if you are worried about what AR they have, just make them read each other book, this will make their AR to be 8, which would be enough to get the ending

^
In response to darksun

Reading each others books right before the ending would actually keep you from getting the ending you want. It resets their AR to 8. 9 or above is required for their ending.

The final AP required to get their ending only happens if their AR for each other is 9 or above, and it then adds +5 to their AR, so after viewing that AP they will have a minimum of 14 AR for each other. Reading their books at that point would bring them way down and would be a huge mistake.

you have to have mavelle to trigger the haute PA it seems, in my game i went with cyuss/phia/t'nique rather than joshua or ashlay, and i did not get the haute PA