Split into two parts, Josh C. Waller’s “Lone Samurai” concerns Riku (Shogen), a 13th-century samurai who washes up on a seemingly deserted island’s beach after a clash with Kublai Khan’s army. In the film’s meditative first chapter, Riku, who’s consumed by visions of his family, prepares to die by suicide. But by the second chapter, when he’s taken prisoner by the island’s cannibals, he turns to killing.