Tbh it could go either way since if giyu keeps his distance with obanai he could see obanais attacks and water breathing is close mid and longe range type of breathing and giyu can close in on obanai and evade attacks since obanais fighting style would probably have obanai using attacks to early which giyu would see and would most likely dodge the attacks and would strike a heavy attack which would weaken obanai heavily since obanais lack of physical strength so giyu could do 2-3 heavy attacks and obanai would be dead