I just saw this posted in /m/, lol. Copypasta from there:
>Well, we've already gone through the whole Setsuna vs. Sousuke thing, and on the whole Setsuna is very much like Sousuke on the outside only, yet Setsuna turns out to be completely different to Sousuke.
>As for Kurz, well... you can't really deny that there's similarities there, either, except Lockon isn't as lecherous and perverted as Kurz.
>As well as many other people, I immediately thought of Matt Engarde when Allelujah pulled his hair back in Ep 25, especially how they both had the whole "let me show you my true self" line.
>Tieria and Keith is one I never thought of, but now that I think about it, it makes a lot of sense. They're both clones (that is, is Regene really does turn out to be Tieria's clone), were both "created" and emotionless yet show emotions later on. They are also prepared to kill their comrades if they disobey orders (Tieria and Setsuna/Al, Keith and Shiroe, etc.). And the fact that they are both so devoted to a supercomputer and go to it for comfort is also a striking similarity (Tieria had Veda, Keith had Mother Eliza), and they both go against them in the end.