I've done an analysis on the characters and determined how they're related to the characters from PS1-4.

(SPOILER)

Ethan=Chaz
Ethan's Father= Alis Landale
Karen=Alys
The relationship between Mirei and Karen=The relationship between Nei and Neifirst
Leo=Odin (PS1), Rudo (PS2), and Gryz (PS4)
The Communion of Gurahl= The religion of the Dezolisians
Parum=Parma
Moatoob=Motavia
Neudaiz=Dezolis
Dulk Falkis=Dark Force
Revolt Magashi= Lord Zio or Lassic
Hyuga= Hahn
Guardians=The Hunters Guild
Locaim Nav= a combination of Raja and Grandfather Dorin
Newmans= Dezolisians on the count that the religion of Neudaiz matches the religion on Dezolis.

Apperently, when they made PSU they did to PS1-4 what XenoSUCKga did to Xenogears. Only this time they didn't hurt the gameplay.