In the early days of the series for various reasons, cast members of a Sentai needed to be replaced mid-season. Sometimes it was for health reasons, scheduling conflicts or contract disagreements. Fortunately, there is story precedence for this that came even before the Super Sentai series.
In 1971, the original actor for Kamen Rider/Takeshi Honga, Hiroshi Fujioka, was injured while performing his own stunts. Needing a replacement, the writers created a second Kamen Rider, Hayato Ichimonji (played by Takeshi Sasaki). When Fujioka had recovered enough, he returned and the show was graced with two Riders. They have since become known as Kamen Rider Ichigou (or Kamen Rider 1) and Kamen Rider Niigou (or Kamen Rider 2).
With that successful switch under their belts, Toei could use a similar swap when things went badly for a cast member in the Super Sentai Series. The first time this happened was actually during the very first series, Himitsu Sentai GoRanger from 1975.
I am not sure of the real life reasons why it happened but the original KiRanger (played byBaku Hatakeyama) left for a short time. The in-story reason was that the character, Daita Oiwa, was promoted to the head of the Kyushu branch of their organization, EAGLE. He was replaced by Daigora Kumano (played by Jirō Daruma) from episodes 55-67. The original KiRanger is forced to return after Daigoro is killed during a fight with a particularly strong member of the Black Cross Army.
The second time Toei had to replace a hero was in Battle Fever J, where they had to do it TWICE!
Let’s talk about the first member to leave the team. Diane Martin (played by Diane Martin) was seriously injured in a fight with a Dracula monster and was forced to return to the United States. She was replaced by Maria Nagisa (Naomi Hagi), a fellow FBI agent who had originally been groomed to be Miss America but when EGOS attacked while Diane was in Japan and Maria was away, Diane took the role until her forced retirement.
Again, I do not know the actual reasons for the replacement but I can hazard a guess. Diane Martin (the actress) did not speak very good Japanese and all of her dialogue had to be dubbed over by Lisa Komaki (who played Peggy Matsuyama/MomoRanger in Himitsu Sentai GoRanger) and voice actress Keiko Yokozawa. This may have added to production times and the cost of production as the staff would have had to take time to re-record dialogue and pay the dub actresses. It may have just been more economical to replace the on-screen actress with someone who spoke better Japanese. Again, this is only my guess based on the facts I have.
The second hero to be replaced was the original Battle Cossack. This one I have absolutely no information on behind the scenes. In story though, Kensaku Shiraishi (played by Yukio Itou) was killed in episode 33 when out of uniform and trying to defend someone from an EGOS attack. His friend, who also worked for the Defense Ministry, Makoto Jin (Naoya Ban) took over the role. He was never much of a team player though and preferred to work alone as an expert marksman. Never much to chat, Makoto was serious, stern and all action and few words, a stark difference from the rather charming Kensaku.
This brings us to the first time the leader of a team was replaced. In 1981′s Taiyo Sentai Sun Vulcan, the original Vul Eagle, Ryusuke Ohwashi (Ryūsuke Kawasaki) left the team in episode 23 to pursue a career as a Space Shuttle pilot with NASA in the United States.
He was replaced by Takayuki Hiba (Takayuki Godai), who was a colleague and a master of Kendo. As such, he brought a traditional katana into his arsenal and used it quite extensively in combat against the forces of Black Magma.
Behind the scenes, Kawasaki left the series to return to his full-time job, which payed better and had more security than working on a children’s TV series that would only last a year.
Fast forward a few years and we come to 1984′s Choudenshi Bioman and one of the more controversial changeovers from one hero to another. When the show began, Yellow Four/Mika Koizumi was played by Yuki Yajima.
However, there was a lot of turmoil behind the scenes involving pay and working conditions. Yuki left the series and not on good terms, not even staying long enough to be replaced. That is why when episode 10 comes around and she is killed, we never see the character out of costume for the entire episode. She is even buried in her Yellow Four outfit.
In the very next episode, we get introduced to her replacement, the Olympic archer Jun Yabuki (played by Sumiko Tanaka). Jun is eager to join the team, a contrast to her predecessor, who initially wanted nothing to do with being a hero. She is at first rejected but when it is discovered that she is descended from the same group bathed in Bioparticles 500 years ago, she is allowed to join.
That was, at the time of this writing, the last time Toei has had to swap out a main character mid-season. Either the contracts have gotten better or the quality of stunt work done by the suit actors and stand-ins has kept the main cast from suffering injuries. Either way, teams have been a lot more stable since the mid-1980s and continue to be so up until the modern day.
I hope this was fun to read or at least a bit educational. If you take nothing else from it, I hope you learned that if you have to join a Sentai team, skip Battle Fever J, they have a freakishly high casualty rate!