Originally Posted by
Bloodline666
Well, when Akuma does his Shun Goku Satsu, he basically drags his victim to Hell, and a :skull::skull::skull::skull:load of demons strike both the user and the victim. Apparently, the potency of it depends on the severity of the attrocities committed by the user and/or victim, thus not only endangering the victim, but also the user. Because of this, Akuma cleanses his mind of all anger, guilt, hatred, and desire through meditation before he uses this move, so that means his sins are basically cleared, and thus, he is unaffected by the move. According the the Street Fighter storyline, only one person aside from Akuma has ever survived the Shun Goku Satsu, and that is Gen, and he survived it the same way Akuma always survives it when he performs it.
Therefore, despite the fact that Sephiroth nearly destroyed an entire planet, he still has a disadvantage, due to the very nature of Shun Goku Satsu. If Akuma was able to kill Bison with it, there's no doubt he'll be able to kill Sephiroth with it, regardless of whether he's in his normal form or "Shin Akuma" form. After all, Sephiroth has committed more than enough attrocities to kill him once and for all should he fall victim to the Shun Goku Satsu.