One great 'Power Rangers Turbo Crossover Fanfiction' is 'Turbo Rangers in the Dino Thunder World'. It combines the elements of both series really well. The author does a great job of making the Turbo Rangers fit into the Dino Thunder setting, and there are some really cool battles and character interactions.
You could also have an OC that is a tech - genius. This character could create new weapons or upgrade the existing Zords. They might be a bit of a loner at first, more interested in their inventions, but then they get drawn into the Power Rangers' world when they realize their creations can be used for good against the evil forces.
The appeal of 'Power Rangers Turbo Crossover Fanfiction' lies in the combination of different Ranger teams. It's exciting to see how the Turbo Rangers would interact with other Rangers from different series. For example, seeing their powers work together or clash.
One idea could be a story where the Accel Changer is stolen by an evil villain who wants to use its power for his own dark purposes. The Power Rangers Turbo then have to embark on a dangerous mission to retrieve it. Another plot could involve a new ranger who discovers an ancient form of the Accel Changer and has to learn how to use it while also fitting in with the existing team. A third idea might be that the Accel Changer malfunctions and gives the Rangers some unexpected and wild powers that they have to figure out how to control in order to defeat a new threat.
One idea could be the Black Ranger getting lost in a parallel dimension. He has to use his skills and wits to find his way back home while facing new enemies and making unexpected allies. Another plot could involve him losing his powers temporarily and having to rely on his martial arts training to protect the city.
One idea could be the OC White Ranger coming from a different dimension where the rules of being a Ranger are slightly different. Maybe in that dimension, they have a special power-up mode that no one in the Turbo team has seen before. This could lead to interesting training sessions and the other Rangers being both amazed and a bit jealous.
In an Accel Changer Power Rangers Turbo fanfiction, I think Cassie Chan would be a popular character to feature. She has a strong will and determination, and seeing how she interacts with the Accel Changer could be fascinating. Another character would be Carlos Vallerte. His kind heart and loyalty could be put to the test with the power of the Accel Changer. Also, Ashley Hammond. She's a smart and capable ranger, and perhaps the Accel Changer could give her some new abilities that she has to master. These characters already have their own fan followings, and featuring them in a story with the Accel Changer would likely attract a lot of readers.
Develop a really unique backstory for your OC. If your OC has a tragic past or a really strange origin, it will make them more interesting. For example, if your OC was experimented on by the same villains the Power Rangers are fighting, and that's how they got their powers.
You can start by giving the OC White Ranger a distinct personality trait. For example, if they're super confident, show it in how they interact with the other Rangers and face challenges. Maybe they're always the first to volunteer for a dangerous mission because they believe in their own abilities so much.
First, start with his flaws. Maybe he's too impulsive at times. Then, have him face situations where this impulsiveness gets him into trouble. As he realizes his mistake, he can start to work on being more patient. For example, in a battle, his quick actions might lead to a teammate getting hurt. This makes him reevaluate and grow.