Sure!

 You can look at the wikia page [url=http://StarOcean.wikia.com/wiki/Star_Ocean:_The_Last_Hope]here[/url], paying attention mostly about Roak and the role and history of the Eldarians, OR you can read a summary here (and use the wikia page if you want to know more.)↓↓↓↓

[hider=Brief-ish summary of the relevant stuff] Eldarians before and during the events of Star Ocean 4 are facing an incredible crisis: The imminent destruction of their home planet by an rapidly expanding red giant. They genetically engineer their children so that they can survive in the harsh conditions.They constantly explore space, searching for a hospitable planet of which to colonize. They have discovered the planet of Lemuris, but are unwilling to disurb the inhabitants or give up their technology as of yet. *Eventually some will move to Lemurius*

As for the planet of Roak, the roleplay happens on the central continent, the Astralaian Continent( The other two being the eastern Muan continent and the western Silvalant continent) The timeperiod for this rolepay is a century before the events of Star Ocean 4, so the Church of Synodai that worships the Archfiend is fairly small. (The same Archfiend that is the focus in Star Ocean 1 if I'm not mistaken.) 

This is the minimum requirement you need to know about Star Ocean 4 to participate.[/hider]