Giyu is an endgame boss in Project Slayers, and he can be a challenge thanks to his Water Breathing combos and the two Mizunotos that keep spawning around (they can be very annoying). You can check our Project Slayers map for his location, but essentially you will find him in the Wilderness in front of Butterfly Mansion.
If you are having a hard time against Giyu there is a way to make your life much easier. First, make sure to lure him away from his Mizunotos so that you will stop aggroing them. Next, each time you are low on health, you can climb up the hill that is really close to Giyu to regenerate your health and spam him with ranged attacks, once your health is back to almost full you can jump down and combo him. Giyu’s attacks won’t be able to reach you up there.
Keep repeating the process until you take Giyu down.