They are fighting each other 1-on-1. Sephiroth can't transform but Sasuke (shippuden) can. No instant death moves but everything else fair game. Who would win?
" @OmegaMekix said:we are only stating the facts" Ok, no more comment. I'm sorry I seriously underestimated Sephiroth, no more rubbing it in. End of discussion, thanks for participating. "Eh sorry bout that buddy didn't mean to do that :( "