One idea could be that the reader is a time - traveler who accidentally gets stuck in the Dragon Ball universe during Goku Black's reign. Another could be that the reader has a special power that Goku Black is interested in and tries to manipulate the reader to use it for his own evil plans. Or perhaps the reader is a Saiyan from another planet who Goku Black sees as a potential ally or threat in his quest for universal domination.
Well, a plot could involve the reader being a healer in a world ravaged by Goku Black. The reader tries to hide their abilities from Goku Black at first, but he eventually discovers them. He then forces the reader to heal his minions in exchange for sparing the reader's loved ones. As time passes, the reader starts to understand Goku Black's motives more deeply and tries to change him from within. It's a story full of tension and moral dilemmas.
A possible plot for a Goku Black x Reader fanfiction is that the reader is an ordinary human living on Earth. One day, Goku Black appears in the reader's town. Instead of immediately attacking, he's intrigued by the reader's unwavering kindness in the face of fear. He starts to follow the reader around, which terrifies the reader at first. But as they interact more, the reader begins to see a glimmer of something other than pure evil in Goku Black, and this forms the basis of an unexpected relationship.
One idea could be that Goku and Goku Black are forced to team up against an even greater threat from another universe. They start to understand each other's fighting styles during the battle and gradually develop a grudging respect for one another.
One idea could be exploring their relationship in an alternate universe where they succeed in their plans. Another could be a story where Goku Black has a change of heart due to his connection with Zamasu and tries to stop their destructive ways. Maybe a plot where they face a new enemy that forces them to reevaluate their alliance.
One idea could be that they discover a new realm together and have to face an unknown threat there. Their combined power might be put to the test in ways they never expected.
One idea could be that the OC is from a different dimension and has a unique power that Goku Black is intrigued by. He decides to use the OC to further his own evil plans at first, but then starts to develop unexpected feelings. Another plot could be the OC being a time traveler who tries to stop Goku Black's rampage, but gets caught in his web of lies and manipulation. A third option is the OC is a Saiyan hybrid who is initially on Goku Black's side because she is misled by his false charm, and then has to face the truth and make a difficult choice.
Maybe the goddess has a prophecy about Goku being the key to saving her realm from an ancient evil. So she forms a bond with Goku, and as they get to know each other better, Goku starts to develop feelings for her. Their relationship then becomes a driving force for him to fulfill the prophecy and defeat the evil, all while exploring the unique aspects of their two different worlds.
In a fanfiction, there could be a scenario where an ancient prophecy foretells of a combined power of Trunks and Goku being the only thing that can stop an impending doom. They start training together to master a special fusion technique that no one has ever attempted before. Along the way, they face challenges not only in their training but also in dealing with their own egos and differences in fighting styles.
Perhaps in a different universe, Turles and Goku are brothers. They grow up together, training side by side, but then a prophecy divides them as they are told one must defeat the other for the greater good. This creates a complex relationship full of love, rivalry, and moral dilemmas.
A really interesting plot could be set in an alternate universe where Goku and Launch are arranged to be married for some political reason in the Saiyan or Earthling world. They start off not really liking each other but as they face challenges together, they fall in love. For example, they have to deal with a group that is against their union and in the process, they learn about each other's strengths and weaknesses.
One plot idea could be the reader being a new servant in the Phantomhive manor. Ciel is initially suspicious but as time passes, he starts to trust and rely on the reader in a unique way. Maybe the reader has a special skill that helps Ciel in his investigations or in dealing with the other nobles.
One idea could be that the reader is a new undertaker's apprentice. They start off being clumsy and Undertaker finds it both amusing and endearing. As time passes, a deep bond forms between them, and they face various supernatural challenges together in the world of Black Butler.