Sorcerous Stabber Orphen: The Wayward Journey Volume 5 by Yoshinobu Akita

Orphen is invited back home by an old associate named Leticia. There he encounters a mysterious, incredibly talented assassin... A sorcerer clad in black, who wields prodigal power. There's only one problem. The assassin calls himself "Krylancelo," and is physically identical to our titular hero. Orphen is pushed to the limit, forced to overcome the greatest challenge of all... Himself.