Suigetsu wins, mid diff. This matchup is actually really funny to me. It's funny because both of them will have a hard time killing the other. Suigetsu is immune to physical attacks thanks to his liquify technique, meaning if Hidan slices him with his scythe, it will go right through Suigetsu's body and collect water, not blood. This means in this matchup, it is impossible for Hidan to use his curse. On the other hand, Hidan is Immortal. Physical attacks have little to no effect on him at all, and can't kill him. The only way for Suigetsu to win is to severely dismember or decapitate him, or trap him in some other way, like with a water prison. It's also worth mentioning that the terrain gives Suigetsu a big advantage with a huge amount of water. Suigetsu's weakness is lightning style, but Hidan doesn't possess any, let alone other ninjutsu. Hidan can't hurt him at all. It might be a long battle, but eventually Suigetsu would win, most likely by cutting him into pieces with the executioner blade.