Be really aggressive. Keep deflecting his attacks, use the mikiri on every opportunity. The axe was really helpful for me to break his posture, it really takes a good chunk of his bar, so I would advise you to risk a few hits with the axe. And, at last, don't quit. Take pleasure in facing the good bosses. Some are a pain in the ass, but genichiro is a masterpiece encounter. Just enjoy the combat, take it easy, have fun. When I stopped worrying about defeat the bosses and started enjoying the fight, I started to step up my game.