Board Thread:Naruto Discussions/@comment-28869806-20160507232833/@comment-4912646-20160509024601

I figure the one arm thing is just his form of atonement. Naruto apparently wears bandages on his arm to symbolize his bond with Sasuke, so I guess Sasuke just takes that symbolism one step further. Personally, I'd rather see him use Susanoo's arm in place of his left like he does in that one Storm 4 ultimate.