Burning thought
Restricted
ahh, a little more interesting a fight, first what do you mean about normal soul reaver? theres just the soul reaver, there isnt another version, but now hes got all his powers, this would be a fairly good match, although you have not specified Kain as immortal in this battle, ill assume he is not completly immortal and cannot return if he is killed first, also ime not sure but in this fight, is kain allowed his chaos armor? in the following battles, i assume he doesnt have it
Chaos Vincent & Omega weiss
should be a fairly simple battle, the guys from what ive seen are simply speed demons, thats about it, personally ive seen no true incredible power from either of them, kain could easily use a time reaver spell, then impale both of them or shield himself, then launch incapaicate bolts to his hearts content, but i do not know their specifics, do they have blood (their not all cells like sephiroth this time if ime not mistaken) if so he could kill them both with a blood shower spell to rip all the blood out of them
Sora+ Riku
i dont know enough on them tbh to make a fight on these guys, please give info? i assume since you put them before Xemnas and Roxas they must be weaker
Twilight Xemnas & Roxas
this should be similiar, Roxas i dont know, but Xemnas i know, he is no match for kain, kain can walk through boundies of dimensions and escape any trap Xemnas creates for him, i dont know if he has blood but a could reaver impalement wouldnt help him, nor would a time spell and energy bolts and lightning
two AC sephiroths
once kain puts his shield up their gonners, they have no real power that can harm kain and few powers htat would even stop him, with all materia and abilities including summons? Kain would easily disect these two Sephiroths, even if their faster their speed will not mean nothing trapped in time, or slowed in kains AOE time reaver spell, in this he will use Dimension reaver to port to both of them and they will be blasted to pieces after several reality warping slashes that make them both take hte same hits, they would be hit by many reavers at the same time, Kain could use TK, their long casting heavey hitters are too slow for kain, he would with a hand movement send them away and interupt their casting, he will have a shield up making all spells reflect back on them, his shield is so easy to cast, i dont think he even moves his hands to cast or speaks a word, its just up on a whim
Raziel
endless fight imo, especially if their both immortals, if their not and they can both die, then i think Raziel will quite easily fall since kain according to your rules has not many powers taken from him which means he has most of Raziels powers as well since Raziel joined with him and gave him his own powers within kain , i dont think Raziel can beat a serious and blood lusted kain anyway even if kain does not have these powers for these fights, i feel he is faster, Raziel is more agile but with less useful reavers imo, i mean hell slowing time to a crawl or creating an Earthquake, in a 1v1 fight, i choose slowing time "shrug"