An otherwise throwaway encounter in Defiance: Raziel runs into a group of vampire hunters, one of whom spots him and yells, "Monster!" Another of the hunters turns, and asks "Where?" Cue Raziel jumping into the frame, looking as pissed as ever with the Soul Reaver manifested, answering, "Here."
The scene from the very ending of Defiance where Raziel shows Moebius that he's been worshipping a Lovecraftian Horror all along.
Raziel: Do you see it now? The monster that you served? Is this what you imagined when you worshipped it?
Raziel: And in that knowledge, go - and feed it. I release you.
And right after that, when Raziel allows himself to be absorbed into the Reaver, truly restoring Kain as the Scion of Balance.
Raziel: The Soul Reaver - pure of all corruption - this is what it is for. This is what I am for. The two become one - both Soul Reavers - together - and the Scion of Balance is healed. And I - am not your enemy - not your destroyer - I am, as before, your right hand. Your sword. And now you will see - the true enemy...
Kain's final confrontation with Moebius at the end of Blood Omen.
Moebius: Aye - you have seen my plan, vampire, as I have seen your destiny: the future says you die!
Kain: Is there a crack in your omniscience after all, Moebius?
(Moebius frantically activates his staff, to no effect.)
Kain: First your omniscience, and now your powers. You're slipping badly.
Moebius: This is not possible...
Kain: The part of me that staff affected is no longer in its place. But you already knew that, didn't you? I always was considered heartless. And now, Moebius, it is time.
Moebius: To kill me? Again? Your only solution, for every problem: kill-
Kain: This is not a debate. You see, this time, you have nothing that I want.
(He grabs Moebius by the shoulder and runs him through with the Soul Reaver.)
And all the while he has a grin on his face. The only time in the entire series that Kain is smiling. And it is magnificent.
The moment immediately after that in the astral plane, as the soul of Moebius picks himself up off the floor, Raziel is right behind him, Soul reaver drawn."OH, SNAP!" And the look on Moebius' face when Raziel runs Moebius through with the spectral Soul Reaver, revealing to Moebius for the first time the true face of the god he had served for centuries is priceless.
The moment in Soul Reaver when Raziel first finds the tomb of the Sarafan lieutenants, including himself.
Almost any scene between Raziel and Kain is a dialogue triumph, but the final confrontation of Soul Reaver, recreated with stunning graphics in the opening FMV of Soul Reaver 2, is endlessly memorable.
The scene with them at the uncorrupted Pillars of Nosgoth, too, is probably one of the best moments of the entire series.
Kain battling the freakin' ELDER GOD and kicking It's ass! Seriously, can anything measure up to that, short of actually killing it?
The dialogue beforehand:
The Elder God: You may ponder the futility of your ambitions as you spend a deathless eternity beneath a mountain of rubble. You and your Soul Reaver will go equally mad as the eons pass: the Citadel of the Apostates will become your living tomb.
(One of the Elder God's tentacles begins slithering towards Kain.)
Kain: Your words are heartening...
(He neatly hacks the tentacle to pieces)
Kain: For you would not fear us unless we could truly do you harm!
The Elder God: NO! You are nothing!
Kain:False God... this is the end: the final turn of your Wheel.
I want to point out something which is rather subtle which just cranks that moment Up to eleven: The Elder has existed for an undisclosed period of time, possibly since the world began. In that time, there is no telling how many races have worshiped it and tried to destroy it. For all we know, the Hylden and Ancient Vampires could have just been the latest in a long line. And yet, it remains completely unharmed... Until Kain gets hold of the purified Soul Reaver, and slices through its flesh like as much hot butter.
Even before Kain proves he can hurt it, you just know awesomeness is about to happen by the look in its eye and the tone of voice; the Elder God's weird-looking pupil is dilating and twitching in a way we've never seen before, and even though its words are those of a Badass Boast, we've gotten familiar enough with its voice to know that its composure is cracking, and it really is scared.
The paradox scene in Soul Reaver 2, when Kain calls out to Raziel to fight fate's impulse, ending with the aversion of You Can't Fight Fate by sparing him, changing the entirety of history from that point in one move.
It ain't just that. Kain risks everything on Raziel listening to him, knowing that in all likelihood he will die and history won't change. He still risks it, and you can see his fear during the monumental moment - he actually cowers for the only time in the series.
The climax of Blood Omen 2 despite being a Disappointing Last Level has a particularly badass moment for Kain. When the Sarafan Lord is threatening him with the Soul Reaver at the gateway to the demon dimension, with Kain only protected from its devastating power by the Nexus Stone the Sarafan Lord tells Kain that while he is currently protected, he can't defeat him without sacrificing that protection. He then starts some textbook Evil Gloating about how they are at a stalemate, which he is sure to win eventually because he has all the time in the world, only for Kain to reply "But I haven't yet made my choice", before throwing the Nexus Stone into the gateway and destroying his enemies plans, deliberately making himself vulnerable to the most powerful weapon in the known world. Kain may have doomed Nosgoth with his selfish, ego-centric decision to rule it rather than heal it, (or so he believes at the time) but he is definitely not a coward.
The whole Kain vs Raziel battle in Defiance. It just shows just how much character development Raziel has had.