The Pink Ranger could be an interesting character to pair with the Black Ranger. Maybe they have a love - interest kind of relationship where their different personalities clash at first but then they grow to understand and care for each other. Also, a villain who has a personal vendetta against the Black Ranger could be paired with him in a story. This would create a lot of tension and conflict, making for an exciting plot.
Another storyline might involve the Black Ranger having to train a new recruit who has a lot of potential but also a wild streak. This could show the Black Ranger's leadership skills as he tries to mold the recruit into a proper Power Ranger. It could also have some comical moments as the recruit gets into various scrapes.
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.
A great plot might involve the Black Ranger getting lost in a different dimension while on a mission. In this dimension, he has to adapt to new rules and powers while trying to find his way back. He could meet new allies or face enemies that are unique to that place. Also, a plot about the Black Ranger having to train a new recruit who has a lot of potential but also a lot of recklessness could be interesting.
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 great storyline could be the Black Ranger having to face a new, powerful enemy alone. Maybe he gets separated from the rest of the Power Rangers and has to rely on his own ninja skills and inner strength to survive and defeat the foe. Another could be a story where the Black Ranger discovers a new power within himself that has been dormant all this time. It could be a power that has a connection to an ancient ninja legend, and he has to learn to master it while also dealing with the regular threats the Power Rangers face.
One potential ally could be an old ninja master who has been in hiding. The Black Ranger might stumble upon this master while on a solo mission, and the master decides to train him further, becoming a powerful ally in his battles. Another could be a mysterious figure who has the power to control the elements in a different way than the Rangers. They could team up with the Black Ranger to fight a common enemy that is immune to the normal Ranger powers.
One interesting storyline could be the Green Ranger OC coming from a different dimension where the rules of power are different. They have to adjust to the new team while also bringing in their unique combat skills. For example, they might have a special way of summoning their zord that the other Rangers have never seen before.
She could be from a hidden clan. Maybe her clan was in charge of protecting a powerful and ancient artifact. But when the Nighloks started getting more aggressive, her clan decided it was time for her to join the Power Rangers. Her skills with the katana, which she learned from her clan's strict training regime, would be a great asset to the team.
Sky, another ranger from SPD, could be a great ally. They have trained together and share a mutual respect. Sky's skills in combat and his ability to think on his feet would complement the Black Ranger's own strengths well.