One idea could be exploring Homelander's childhood from the perspective of the reborn character. Maybe the character tries to prevent Homelander from becoming the villain he is. Another plot could involve the reborn character using their knowledge of Homelander's weaknesses to try and control him for the greater good. And a third could be that the character is reborn as Homelander himself and has to deal with the internal struggle of his powers and his public image.
One idea could be a new vampire character being reborn in the Twilight universe with a special power, like the ability to control the weather. This would create a whole new dynamic as they interact with the Cullens and other vampires.
One idea could be a story where the protagonist discovers a hidden power within a seemingly weak Pokemon in the Reborn region. This power could be the key to saving the region from a new, mysterious threat.
One idea could be that the reborn character tries to prevent Obito's fall to the dark side. They could use their knowledge of the future to stop Madara from manipulating him. For example, they might intervene during the battle where Obito was thought to be dead and expose Madara's true intentions early on.
Well, a plot could be that the reborn character discovers a hidden power within Kryptonian abilities that no one else knew about. This could put them in a position where they are both feared and revered. Also, they could form an unlikely alliance with a group of Kryptonians who were considered outcasts. Together, they try to bring about a new era on Krypton. Another interesting plot would be the character being sent on a mission to a different planet. Since they are reborn as a Kryptonian, they have unique skills for this mission and face various challenges during it.
One idea could be that the reborn character has to deal with the Hulk's uncontrollable rage in a new way. Maybe they have some special ability from their rebirth that can calm the Hulk down. For example, they can communicate with the Hulk on a deeper level, like understanding his fears that fuel the rage. Another plot idea is that the reborn character uses the Hulk's strength to protect a world that is different from the original Hulk's universe. They might face new enemies and challenges that require both the Hulk's brute force and the character's unique knowledge from their past life.
Maybe the reborn Saiyan has memories of their previous life and tries to use modern - day knowledge to change the fate of the Saiyans. For example, they could introduce new technologies or strategies for fighting that would give the Saiyans an edge. They might also try to prevent the destruction of Planet Vegeta by warning the Saiyans about Frieza's true intentions in a more convincing way than Vegeta did in the original story.
One idea could be that Harry is reborn with all his previous memories intact. He uses this knowledge to change the course of events much earlier. For example, he could start befriending Hermione and Ron in a different way, perhaps by being more upfront about his past experiences and the threats they will face.
One idea could be to explore the backstory of a minor character in the original 'a legend reborn' and give them a major role in the fanfiction. For example, if there was a sidekick who was always in the background, you could make them the key to saving the world this time.
One idea could be being reborn as a new character with a unique Grimm -fighting ability. For example, having the power to control the elements in a way that no one in Remnant has seen before. This would immediately draw the attention of the main characters like Ruby, Weiss, Blake, and Yang. Another plot could involve being reborn into a villain's body and having to struggle with the pre -existing evil tendencies while trying to turn good and help the side of the heroes. Maybe trying to convince the heroes that you've changed and are now on their side.
Well, perhaps the OC reborn as Kurama tries to find a way to coexist peacefully with the jinchuriki in a different way than in the original story. They could use their unique perspective to broker better relationships between the tailed beasts and the humans. Maybe they also try to uncover secrets about the origin of the tailed beasts that were previously unknown.