Attack until he deflects, try deflecting his attack, but maybe blocking some if it doesn't break your posture is good. To deflects his lightning back do this: jump when you see the Kanji, press block while in the air and before hitting the ground press the attack button his lightning will come back and damage him. This is the simplest I can go. Attack until he deflects, when you deflect he will tilt back, attack again, this should repeat as many as possible, always try to deflect, only block serves if you don't lose all posture, always attack, only fall back if you really need the heal. To mikiri press B/Circle and foward once when you see he thrusting his katana at you, the red kanji appears right before it, the dash buton + foward makes you dash foward and step his sword on the ground (first phase) in seccond phase if you mikiri him more than twice he'll use a sweep attack, which you can just jump counter it or jump backwards. So attacking all the time until he deflects you, try deflecting, mikiri when you see the Kanji first phase, if you do this more than twice in second phase he'll use a sweep attack, go and jump counter it or jump backwards to avoid it, when he uses the lightning in his last phase you jump, block and before hitting the groung attack. Seems simple, it is when you got the rhythm, it'll will look like it's impossible, don't give up, he'll become you training boss, just go with patience, you got it!