Yahaba is an endgame boss in Project Slayers, and his Arrow BDA can be quite hard to overcome as he has quite a big range and nice combo moves. You can check our Project Slayers map for his location, but it is best to unlock Ouwbayashi Home by spending one map point (1,200 Wen) and fast travel there using the Horse Guy.
If you are having a hard time against Yahaba there is a way to make your life much easier. You can just climb up a hill and spam Yahaba with range attacks and jump in to combo him. There is a great video by YouTuber Khaiel showcasing this (1:37 mark) and the same trick can be used against Susamaru:
While you are here, don't forget to check our Blood Demon Art Tier List, Breathing Tier List, and Weapon Tier List to set up your character for success in the game properly! We also have guides on how to get Water Breathing, Thunder Breathing, Insect Breathing, or Wind Breathing.
Finally, note that a private server will make your life easier while leveling up.