I'm not a mega-fan of NGE by any stretch, but I have watched the original series, the first batch of films and the most-recent batch of films a couple times over, and something strikes me every time:

Of ALL the characters in the series, from original to remake, the character whose personality and behavior changes the most drastically from incarnation to incarnation is Shinji, Rei, or Asuka.
The three of them all seem to remain RELATIVELY "static" to their original incarnations from the first series. But Kaworu, however, has remarkably different dialogue and even personality changes between all of his incarnations.

And what's more, Kaworu seems to know (from dialogue in Evangelion 3.333 and 3.0 1.0) that he isn't the first version of himself to be involved in these "cycles" with Shinji, and that he likely won't be the last, either. But unlike Shinji, Rei and Asuka, Kaworu seems to adapt and change his tactics and behaviors every time the series is "reborn."

On Earth's moon, we see a seemingly endless line of Coffins for Kaworu; to his right all empty, and to his left, all unopened, and we see him taking notice of this. As if every time the world of "Evangelion" Ends and is Reborn, another iteration of Kaworu awakens, and seems to retain knowledge of the events from the previous cycles, allowing him to not only adapt his tactics, but also to grow as a "human-being."

His personality seems to mature and evolve, from his original iteration seeming almost "child-like" and "naive," with a lack of understanding to why Human-Beings act and feel things the way they do, to understanding the motives of Shinji, who he recognizes as a deeply-damaged and emotional boy.

While his "co-stars," Shinji, Rei and Asuka all seem to follow relatively similar paths in the beginnings of the journeys and arcs, with similar personalities and sometimes even identical life-events. Almost like NPC's during a replay of a game; the only character who truly evolves, and makes different choices, and can potentially affect the outcome of the story because of those choices, is the "Main-Character." Everyone else around him only seems to deviate from those paths as a ripple-effect of other influences, which may or may not be something to do with different choices that Kaworu makes, that we don't fully get to see for ourselves.