This six-movie set (also known as Baby Cart, Shogun Assassin, and Sword of Vengeance) originally appeared in a 110 volume adult comic book series, and was adapted for live action by Shintaro Katsu (the actor that played Zatoichi and later Hanzo the Razor) as a staring vehicle for his brother, Tomisaburo Wakayama.
All six movies were filmed in just two years, but flopped with the Japanese audiences. Strangely, they were far better received by international viewers and are now considered to be classics. Though other films and other actors later depicted the tales of the Lone Wolf and Cub (the best of which is the 1992 Lone Wolf and Child), Ill only address Wakayamas magnificent portrayal here.
These wonderful movies offer psychological and cultural subtleties along with amazing swordplay. They gripped me when I first watched them decades ago, and they continue to mesmerize me when I watch them today (Ive seen all six many, many times, and cant wait to watch them again!).
If you want to play it safe and buy just one, allow me to strongly recommend Baby Cart At The River Styx, a movie that, in my opinion, might well be the single greatest Samurai film of all time.