The costume that Sho Kosugi wears as the ninja villain Okasa is not a traditional one seen in prior films such as Enter The Ninja and Revenge of The Ninja. This one features metal chains around the hooded part of the face and around his calves which resembles more of a knight from the ancient times than a traditional Japanese warrior assassin. The only thing that it has in common with the ninja films is the color, which is black.
In the Episode Kunoichi, in middle of the episode it is revealed that one of the villains was a female ninja in training Allison Grant, a reporter who turned out to be Okasa's student. Sho Kosugi would later after this series aired, would battle of a "possessed" female ninja played by Lucinda Dickey in Ninja 3: The Domination as the good guy not the villain like he was featured on the show.
The show was inspired by the success of Enter The Ninja, which was released in 1981 and starred Sho Kosugi and Franco Nero and was a major success for Cannon Films which would spawn two sequels also starring Kosugi, Revenge of the Ninja and Ninja 3: The Domination and then followed by American Ninja, which would spawn four sequels. Kosugi also had three more ninja films in which he starred in: Pray For Death, Nine Deaths of the Ninja and Rage of Honor.
The Butterfly medallion that Lee Van Cleef wears on the show is a symbol of his family in Japan. If anyone kills Van Cleef was to have been killed on the show, any ninja could've claimed it as a true master destroying his family legacy in the process. The only time that the medallion was taken away from Van Cleef's character was by the female ninja, Allison Grant after her revelation as Okasa's ninjitsu student and wore it before Van Cleef reclaimed it after foiling her assassination attempt in the episode, Kunoichi.
Every episode after the pilot began with a recap of Lee Van Cleef's character backstory with a flashback to the same scene from the pilot episode with Timothy Van Patten narrating and blending into the latest episode.
If the show had continued, Timothy Van Patten would've become a ninja since Lee Van Cleef had been training him almost indirectly in every episode in his own way and already had most of Van Cleef's moves.
Oscar Winner Bill Conti composed the music for the main theme to the show as well as a few episodes would also write the original score to the hit film, The Karate Kid, which was released during the Summer 1984 just as this series was about to end in August of that year.
Ashley Ferrare who was in the episode "Failure To Communicate" was also in Revenge of the Ninja, which also starred Sho Kosugi, who played the main villain in this series. Ironically, her character's name in the episode was also named Kathy not unlike Revenge of the Ninja where her character's name was Cathy.
Kane Kosugi who appears in the shows' final episode is the son of Sho Kosugi, who plays Okasa, the series villain and stunt coordinator. Prior to this they also appeared together as father and son in Revenge of the Ninja, which also featured Ashley Ferrare, who also appeared on the show.
Ninjas are trained to be invisible. However in this show, Lee Van Cleef's character is often seen in his ninja uniform in public such as a Halloween party in "Out-Of-Time-Step" and "Kunoichi" where he is arrested and his picture posted on the front page of a newspaper and interrogated in his uniform.
The show starts out with a glowing Ninja star (Shriken) in red, which is the same one that Okasa (played by Sho Kosugi) throws in the pilot episode hitting John Peter McAllister (played by Lee Van Cleef) in the back and the same one that he carries around and then gives to Max Keller later on.
The trivia items below may give away important plot points.
Okasa's (played by Sho Kosugi) back story is that he is a former pupil of John Peter McAllister (played by Lee Van Cleef) who is out to kill him and become the master ninja after McAllister decides to leave Japan to search for the daughter he never knew he had in the United States. Which explains why he appears wherever McAllister and Max travel to and always attempts to kill him.
When Lee Van Cleef is fighting someone on the show, you almost immediately tell that it is Sho Kosugi in his place. The way you can spot it is by his height, his poses, his eyes and his yells. Van Cleef does not do any of these during his fights with Kosugi as Okasa.
The series ended without anyone knowing who was John Peter McAllister's daughter really was and never appeared on the show in person. The closest was the character played by Janine Turner, who was an actress posing as his daughter in a blackmail scheme. The other closest time was the New Orleans episode where his daughter was an informant in a black arms deal led by shady businessman Robert Pine.