they are of the same creator...and also what he says,in each game some characters of other games appear...for example,en star ocean,valkyrie preofile and radiata stories,gabriel celeste and ethereal queen aways appear as bosses...in radiata stories,you can get lenneth valkyrie(from vp lenneth,and vp1),you can get clou outfit(with the bloue wig and his clothes)...in vp you can fight ethereal qwueen and gabriel celeste(the same in radiata),and dirna hamilton appears...in star ocean,you can fight ethereal queen and gabriel celeste and also fight freya
valkyrie
finnally i finnished seraphic gATE!!!!!!!! now i have alicia Freya
Brahms
iseria queen was reaaaally easy to beat,but then i had to kill dirna hamilton(serious mode) and she was a real pain,cause she had a lot of h´p,magic power and also 3 shadows helping her...also,i didn't train valkyrie (i had alicia,brahms,hrist and freya at level 99,but valkyrie at level 55,so i had to revive her constantly)
now,i finnished off lezard by the forth time,and i started the game afterwards with more difficulties...but i have more music,i can put vp 1 battle music and i'm trying to do things i didn't(for example get the bahamut tear,valkyrie favor,philosopher book,etc...you have to do some things before ending chapter 3 and 4)