He’s found inside the dojo, right in front of the Upper Tower - Ashina Dojo sculptor’s idol. This is an optional boss that you can skip but defeating him will give you easy access between the main boss Genichiro Ashina’s location and the castle’s Dojo sculptor’s idol.
How to defeat this boss?
He has lightning-quick reflexes and long reach, thanks to his quick-step and quick-draw skills. With his sword sheathed, always anticipate him using a quick-step forward immediately followed by a double-slash. While you can block this attack, side-stepping and counterattacking is a better way of landing hits on him.
One tactic you can use is using the Chasing Slice skill. With this skill, you can throw a shuriken then immediately make a follow-up attack. He will block it and will attempt to counter-attack with a perilous swipe/slash. Jump at the right moment to land free hits on him.
You can use combat arts on him but preferably, use something quick and won’t leave you open like Shadowrush. Use your combat art as a counterattack since attacking aggressively will just allow him to deflect your attacks and perform his own counterattacks. As mentioned before, he’s open to quick counterattacks right after he performs his quick slashes or perilous attacks.
* Prayer Bead * Read the scroll on the wall to learn the Lightning Reversal skill. It will not be listed in your skills list but it will be helpful in the battle against Genichiro Ashina so make sure to take note of this mechanic.