First thing you need to do is to get closer to the boss in a burning house and throw the Fistful Ash on to the enemy boss so that he will not be able to summon the annoying dogs.
Follow the steps below if you want to take down the Lone Shadow Masanaga from three years ago.
Then exit the building and run straight towards a bridge. Wait there sometime for the boss to come, But he will not come there. You have to again go back to that burning house.
Kill an assassin on the bridge and head back to the house.
Slash the boss with the help of a red sword. The attacking range of the red sword is just on the next level and you will counter the boss just in a few lusty blows.