Fight takes place in the place where Kisame fought Killer Bee
Kisame could just substitute when Black Star tries coming at him, or just flood the area... Not just that but Samehada is capable of healing wounds (Got his entire torso torn off by KB but still managed to regenerate his flesh back.)
And once Kisame floods the area it's game over for Black... Clones, Substitution, Shark Bombs, and possibly being torn to shreds by Kisame himself.
I see BS/Tsubaki taking this more times than not. With certain techniques BS' speed could become far too much for Kisame to handle and with his soul attacks it could give him an instant win. I can't recall any attacks from Kisame that could really harm BS. And even if Kisame chooses to flood the place, BS has shown to be capable of fighting just fine underwater, plus water amplifies his soul attacks.