On the one hand, the battle is very difficult, due to the sheer strength of his attacks. On the other, however, with a bit of patience, you can defeat him and take minimum damage. The important thing is to get before the battle a weapon, which deals high damage, and armor with high defense level. If you want to make sure that you defeat the samurai without the necessity to wait for the stroke of luck, you simply have to follow several rules.
Keep at a medium distance of the opponent. Observe how he swings his axe and attack only after he slams it into the ground. Then, you will have a moment to dash up, deal a single blow and get away. This is why, the best weapon here is either a battleaxe or a sledgehammer. Sometimes, after he summons his guardian spirit, the boss jumps up into the air and hits the ground, which generates lightning. You only have to get away to a safe distance. Around the middle of the battle, the samurai swaps to sword and speeds up his attacks, which may be dangerous. You only have to wait it out, by walking around one of the pillars. When he returns to his previous weapon, you return to the above tactic.