I don't have clear one thing about the Raiden/Solidus relation.
They were chosen because their relation was similar to the one of Snake with Big Boss, but it seems it's only for MGS2 plot, not for the events preceding the game. I mean, is it their relation similar to the one of Solid with Big Boss because they were "forced" to this kind of relation when Raiden was only a kid, or the relation they had was "born naturally" and then it was used only later by the Patriots for their experiments (the events of MGS2)?
I hope my question is clear