Born around 1550 on Izu Oshima island, originally named Maeda Kagehisa. He grew up on the remote island, then left to pursue the way of the sword. Traveling across Japan seeking duels, he reportedly fought 33 life-or-death matches without a single defeat. His swordsmanship centered on "itto ryodan" — decisive single strikes that subdued the opponent with one cut, a rational style stripped of all excess. He systematized this philosophy into "Itto-ryu" (One-Sword School), which became one of the most influential sword schools in Japanese history. It spawned numerous branches including Ono-ha Itto-ryu (through Ono Tadaaki), Mizoguchi-ha Itto-ryu (through Ito Tadanari), and Hokushin Itto-ryu (through Chiba Shusaku). His student Ono Tadaaki became sword instructor to the Tokugawa shoguns, making Itto-ryu, alongside Yagyu Shinkage-ryu, one of the two officially recognized sword schools of the shogunate. Many modern kendo techniques are said to derive from Itto-ryu, including foundational strikes such as "kiriotoshi" and "men-uchi." In his later years, after passing the school's orthodox lineage to Ono Tadaaki, Ittosai vanished without a trace. Some accounts say he became a monk, others that he wandered the provinces, but his ultimate fate remains unknown. This mysterious disappearance has itself become part of his legend. He appears in the manga Vagabond, the Samurai Dou game series, and other creative works, and remains one of Japan's most widely known swordsmen.