"Episode XL: Jack vs. the Ninja" is the fortieth episode in the fourth season of Samurai Jack. The episode features Aku sending the Ninja, a deadly assassin, to kill Jack, who must use his own martial arts to survive.
As the episode opens, a ninja silently infiltrates a large Japanese temple where Jack is at prayer. The ninja sneaks up behind Jack and, before the Samurai can react, slices him in two. However, Jack is revealed to be a robot; the entire attack was merely a training exercise. Aku appears to congratulate the Ninja for passing his test before sending him to kill the real Jack.
Jack travels through a dense jungle, being stalked by the Ninja all the while. The assassin finally sees his opportunity, but before he can strike, a boy races through with giant robotic lobsters chasing him. Jack rushes to the boy's aid and defeats two of the beasts. The boy tells Jack that more of the lobsters are attacking his village. Jack has the boy lead him there, still unaware that the Ninja is following him.
Upon reaching the boy's coastal village, Jack destroys a whole horde of robotic lobsters while the Ninja watches from the roof of a hut. The final opponent is a particularly massive lobster, but it only lasts slightly longer against Jack before meeting the same fate as its brethren. After the battle, the grateful villagers shower Jack with praise and gifts, but the celebration is halted when a woman cries out; the Ninja has taken her son to a nearby ruined tower.
Inside the tower, Jack finds the boy tied up and hanging from a beam. As he climbs up to free him, the boy's eyes widen with fear. Seeing the reflection in them, Jack narrowly avoids the Ninja's ambush slash. He quickly finishes freeing the boy before turning his attention to the Ninja, fending off its hit-and-run attacks from the shadows. Jumping onto a higher beam to catch a breather, Jack identifies his foe's technique, revealing that he has been trained in a similar fighting style; one that uses the light instead of the dark.
As Jack adjusts his attire into pure white ninja garb, the Ninja climbs up to his position and attacks; by the time he strikes, the samurai has vanished, using the light to disappear just as easily as the Ninja uses the dark. The two warriors duel across the tower, using the shadows and sunbeams to their advantage. However, the sun begins to set, slowly filling the battlefield with darkness. Jack eventually finds himself at the very top of the tower, with barely enough light left to hide in. Sensing victory, the Ninja moves in for the killing blow.
However, the Ninja's leap onto Jack's beam causes it to shake slightly, betraying his position to the samurai. Jack immediately uses his sword to reflect the sunlight into the Ninja's eyes, leaving him open for a sword toss that destroys him at last. The episode ends with the boy running to Jack, hugging him as a sign of gratitude as the sun fully sets.
- Casting by
- Collette Sunderman
- This episode is sometimes erroneously referred to as "Samurai versus Ninja" in fan circles.
- The same scream is reused three times for the boy while he's in the jungle, with the first fading out.