Shigurui ã‚·ã‚°ãƒ«ã‚¤ (Madhouse Production)
Summary from anidb
Based on a seinen manga by Yamaguchi Takayuki, serialised in Champion RED.
We are in the sixth year of the Kanâ€™ei era (1629), at the beginning of the Edo period. The story takes place inside the castle of Suruga.
The first duel of a tournament which, in contravention of all existing laws, allows the use of real swords, brings together for the last time two mighty swordsmen whose intertwined past is as beautiful and gruesome as the wounds upon their bodiesâ€¦
An exceptional manga artist decides to tackle the forbidden work by the last giant figure in samurai literature, only to give birth to a colossal period drama filled with unspeakable tragedy and cruelty!
This is a violent one so be warned if your squeamish and nsfw due to sex scenes and the detail they put into the anime alone. After watching the first episode this has some very good potential.