At its beginning, Super Sentai was one of the few tokusatsu franchise including female superheroes, who could change into superpowered suits to fight enemies. Among early Superheroic female characters in toku, Bijinder from Kikaider 01 was one of the first ones, and at the same time that the first sentai series, Himitsu Sentai Gorenger aired, Kamen Rider Stronger aired as well, with Tackle being Stronger's female sidekick, who was able to change into the ladybug-looking Tackle suit. However, while Tackle was Stronger's assistant, in Gorenger, Peggy Matsumoto/Momoranger was an equal partner among the five Gorenger. Since then, (with one exception) Super Sentai always had at least one female hero, and, starting with Battle Fever, villainesses were shown as well. In each series, the female characters had the opportunity to have episodes focusing on them.
However, the importance of those female characters in each series's plot was not the same in the series, either as heroines or as villainesses. I'm gonna review the history of Super Sentai and put emphasis on shows that gave more spotlight to female characters.
1) Early era : Gorenger and JAKQ
As episodic shows without villainesses, no female character had have important roles in the main plot ; but the same could be said for the male heroes as well: the heroes fought the villains as a team, and each teammates was important ; Gorenger also had some female supporting characters, one of them even filling sometimes as Momoranger for Peggy.
2) Late Uehara era: plenty of villainesses
Battle Fever J, Denziman and Sun Vulcan weren't the best series for heroine focus: because of Diane Martin's miscast, the first half of Battle Fever almost forgot it had a female teammate (Maria Nagisa in the second half however, had a more prominent role), and Sun Vulcan didn't even have a female ranger. However, all those series had major villainesses : in Battle Fever, Salome was by far the most active villainesses, often involved in the battlefield and closely working with the Monster of the Week: and Denziman and Sun Vulcan had most of the antagonists being female characters: Denziman's Big Bad was Queen Hedorian, played by Machiko Soga, and her two female agents (Keller and Mirror) were a lot involved in the Vader's evil plans, doing spy work disguising as normal women to carry out their schemes, and leading the Mooks and Monsters of the Week in the fights. Sun Vulcan used the Zero Girls in the same vein, brought back Machiko Soga as a main villainess, and Amazon Killer also had a major villainess role.
3) Soda era: great era for both heroines and villainesses.
The Soda era was a great era for female characters in sentai. Goggle Five and Dynaman had some great lone female rangers (especially Dynaman, with Rei Tachibana/ DynaPink).
But, more importantly, starting with Bioman, the teams started to include two women, and the female rangers were able to wear suits that weren't pink (mostly Yellow, but also White (in Changeman) and Blue (in Liveman)). Many of Soda's heroines are some of the most memorables female rangers, such as Jun in Bioman, Sara in Flashman, Megumi in Liveman and Remi in Fiveman. Soda also always introduced at least one important villainess in his shows. Some of them, like Zenobia in Dynaman, could have major roles.
Among Soda shows, three of them gave especially important roles to female characters :
Changeman had already two great heroines, with Nagisa Sayaka and Tsubasa Mai. However, Changeman can boast having one of the best sentai villainesses of all time : Queen Ahames. Ahames became an important general with very vicious plans as soon as she appeared, but, most importantly, she managed to earn the superpower coming from the Nana's Rigel's aura, at Giluke's expense, and replaced him as the Gozma's main general after Bazoo banned Giluke. She remained a very dangerous enemy, cruel towards her enemies but also her allies until her death, her last act being destroying the Changeman's base. On the good side, a supporting character, Nana had some major plots, like the Rigel Aura plot, and she was also involved in other key episodes, notably the final arc. Another villainess, Shima became the first villainess that changed sides and became an ally, and another supporting character, Zoori, played a key role in making her husband, Gator, defect Gozma as well.
Maskman had two badass heroic ladies with Haruka and Momoko (Yellow and Pink Mask). But, more importantly, the most important antagonist in Maskman was without a doubt Prince(ss) Igam, since the main storyline mostly involved Takeru/ Red Mask and the two Igam sisters, Igam and Iyal, with Red Mask's love story for Iyal, and the bitter hate that Igam had against him as a result. Moreover, Igam and her sister were revealed to be the ones to be able to bring down Zeba, and make the Tube become again a peaceful subterran kingdom.
While Turboranger was one of the few shows of the Soda era with only one heroine (Pink Turbo/ Haruna), it can be argued that the most important character of the second half of Turboranger is the half Boma Kirika, aka Tsukikage Sayoko. Indeed, during the last 21 episodes of Turboranger, not only she was one a major villainesses, she also showed a lot of development during that era. First, she was shown turning from a normal girl into a bitter and cruel enemy. Then, she became a very dangerous enemy, but Soda managed to make the audience feel some sympathy for her, by showing her sad background and her need to find her identity. Lastly, after meeting her Boma father, she realized that she didn't have to be humanity's enemy and after much internal conflict, not only she stopped being the Turboranger's enemy, but she played an important role in saving Yamimaru from himself and become a peaceful man.
4) Jetman/ Sugimura era
While Jetman had two female rangers, a major love story between the main hero and a villainess (the Ryu/ Rie-Maria storyline) and the first female commander (Aya Odagiri), the main storyline still revolved mostly around the male characters (Ryu, Gai, Radiguet and Tran/ Tranza).
Zyuranger had the main villainess being a Big Bad (Witch Bandora) with a major female general in Lami.
Dairanger was notable for having plenty of major subplots, and two of them involved a lot female characters. The first one was the Daigo/ Kujaku arc, which revolved mostly about the doomed love story between Daigo/ Shishiranger and the peacock warrior Kujaku and the rivalry between Kujaku and the Gorma female general, Gara; Gara (or rather, fake clay Gara, was defeated by the spirit of the real Gara, who had become good again). The second one was the Kou/ Akomaru plot, with the involvement of Rin/ Houhouranger as Kou's friend and the two boys's mother.
Kakuranger was the first Sentai series having a female ranger involved in the central plot. Indeed, Tsuruhime/ Ninja White, not only was the leader of the Kakuranger, but she also had the key plot with her father Hakumenroh who was involved with the Yokai against his will.
5) Carranger and beyond
Carranger had two very well done female rangers, with Yellow and Pink Racer, but it also had a key romance plot with Red Racer and the villainess Zonnette, and that romance played a key role, not only as a major subplot, but also because the redeemed Zonnette was the one who made the remaining Bowzock help the Carranger defeat the Big Bad Emperor Exhaust and then, stop doing evil stuff.
After Carranger, while many sentai series had some very well done female characters, either as heroines or as villainesses, few of them became central characters in the series's storyline.
Among those sentai series, however, Abaranger deserves some spotlight because of the major roles of female characters in its storyline. While Abareyellow didn't have much focus compared to her teammates, two characters were pretty much some of the most central characters in the plot: Jeanne/ Mahoro and Lije/ Lijewel/ Mysterious Girl. And the interesting element is that not only they were important as evil characters, but also as good characters.
Jeanne was the most important Evolian general during the first half of the show, having a deep rivalry with Abareblack and involved in the most dangerous Evolian plots. Very quickly, her background (as Asuka's wife) was revealed, and a mysterious girl (in fact, the part of Lije's soul that managed to escape the evil Evolian's god influence) played a key role in stopping Abareblack and Jeanne from killing each other by reminding them of their past. When Abarekiller appeared and became a major antagonist himself, Lije started to get some spotlight as well, since she developed a crush for the evil ranger, playing a key role in him becoming the leader of the Evolian, and then, making herself turn from a little girl to a young woman, and, as a result, become a dangerous enemy herself.
However, at the same time, Jeanne had a final showdown with Asuka/ Abareblack, but, as a result of the mysterious girl reminding her of her past, Asuka telling her of his true love and then Asuka freeing her from the evil armor, she was able to turn back into the good Mahoro. After a few weeks with amnesia, she managed to remember of her past, and decided to become Jeanne again, to free Asuka from the evil armor and then, help the heroes defeat the Evolian by becoming a spy and gving the heroes very important information to defeat the Evolian. Lijewel, realizing that Mikoto was in danger because of Dezumozorya, also played a role in Mikoto becoming at last the heroes's ally, and the Mysterious girl was the one who managed to expel the Dezumozorya from Lijewel's body, saving her (and herself at the same time) from the evil God.
Other series had some key plots involving female character: GogoV had good female characters, with Matsuri/Gopink, the Saima daughter Dinas and GoGreen 's Sempai, Kyoko, and the Big Bad was the mother of the Saima siblings, Grandienne. Yuuri/ Timepink was the leader of the Timerangers. TsueTsue was a major villainess in Gaoranger. Magiranger had a lot of female characters, with the Pantheon Goddess Sphinx having plenty of development. Shinkenger also had a key plot involving a female character, with Takeru/ Shinkenred being the Kagemusha of Kaoru/ Hime Shinkenred.
And of course, the Unofficial Sentai Akibaranger has also most of its characters being female, and as such, having major roles. In fact, Nobuo/ Akibared, while the main character, was one of the very few main male character in the show.