They have come in all types and colors. And their origins have usually followed a certain trend.

Sometimes they were in the right place at the right time.

Sometimes they wanted to join the team ever since they were small, and trained their butts off to earn it.

Sometimes they were trapped in a prison until the current team freed them.

Sometimes they were chosen since birth to bear the power.

Sometimes they were part of a Great Offscreen War where they were presumed dead, but had been placed under some sort of enemy mind control until the current team freed them.

But Ressha Sentai ToQger, like so many other things it is doing differently, has decided on a new approach for Akira Nijino, ToQ #6. He was originally a Shadow Monster, but it seems one day he took a look at how much suffering he had caused drawing darkness out of human hearts, and decided it wasn't worth it. After that, he took on a human form and got a job as a signalman on the Rainbow Line. No Sixth Ranger in Power Rangers or Super Sentai history has ever had origins like that.

3383173 It looks like we've found a sixith ranger to rival the likes of Tommy, Jason, Zane, Eric, Merrick, and Trent.

3383173
You forgot when sometime the villains has them under their control

3384307 No I didn't. I mentioned the examples where they were believed dead in a Great Offscreen War, remember?

3384319
You talking about PR or SS? Because I don't know anything about SS and in PR there were plenty of examples where the Sixth Ranger was being controlled by the villains into fighting the main team.

3384954 Both, but mainly SS.

Examples in both are Gaosilver, who you might know as the Lunar Wolf Ranger, and Wolzord Fire, AKA the Mystic Force Wolf Warrior.

Zyuden Sentai Kyoryuger, which will be adapted into Power Rangers Dino Charge, had another example in the form of Kyoryugold. He was a Kyoryuger 500 years ago, and went missing, presumed dead. But in reality, he had been trapped inside Raging Knight Dogold, a member of the Deboss Army who was a suit of Animated Armor, and always had to have someone trapped in his armor to be able to do anything.

3385028 Sort of like Mike and The Magna Defender in Lost Galaxy.

3385323 Except the Magna Defender wasn't evil. Dogold was.

It was more like Merrick and Zen-Aku from Wild Force.

3385401 Oh yes, I remember that. One of the last times Power Rangers had a compelling story arc and an interesting villan/anti-hero.

Actually the best idea for a sixth Ranger is the idea of a villain defecting, yet its kept vague as to whether or not they're on the level or faking