You could write it so that Jacob Black time travels as a side - effect of a powerful spell cast by an old Native American shaman. This would tie in with his Native American heritage and add an element of mystery and magic specific to his world. He might then be sent on a quest in the different time period he lands in.
One way to write it uniquely is to focus on the magical or supernatural aspects of Stevonnie's pregnancy. Since they are a fusion, there could be some extraordinary things that happen during the pregnancy that are related to their gem powers. For example, the baby could have some sort of gem - related ability even before birth.
There's a fanfiction where Jacob imprints on a time - traveling girl. She's from the future and has knowledge of events that are yet to happen in the Twilight universe. Their relationship is strained at first because she's constantly worried about changing the future. But as they get to know each other, Jacob helps her accept that some changes can be for the better.
There might be a fanfiction where Jacob Black time travels to the era of the first vampires. He could interact with the original vampires and perhaps gain some knowledge that would help him in his own time. This would create a whole new dynamic in the story as he tries to navigate this dangerous and unknown world of the early vampires.
You could incorporate the magic of the Harry Potter world into his treatment. Maybe there are some rare potions or spells that could potentially help, but they come with their own risks and side - effects. For example, a potion that might slow the cancer but also makes him lose his ability to use magic temporarily. This would create a great conflict within the story.
Their relationship could develop uniquely if Paula starts to see Sebastian as a mentor. She could ask him to teach her some of his skills, like self - defense or how to be more observant. Sebastian, being prideful in his abilities, might be initially hesitant but then start to enjoy teaching her. This would create a bond based on learning and growth.
Their relationship could develop through a shared secret. For example, they both have a fear of a certain critic in the ballet world. They bond over this shared fear and start to practice together in secret to overcome it. As they practice, their relationship deepens.
I've read one where Bella discovers a new power as a vampire that allows her to communicate with Jacob telepathically. This completely changes the dynamic between them as they can now share their innermost thoughts and feelings without having to be in close proximity. It also makes their relationship more complex as they have to deal with this new form of connection.
Another good one is 'Back in Time with Bella and Jacob'. In this fanfiction, a magical event sends Bella and Jacob back in time. They face many difficulties, like trying to fit into the past society without changing too much of the future. The story focuses on their bond, which becomes stronger as they face these time - related obstacles together.
In these fanfictions, Jacob often retains his loyalty, which is a big part of his character. He's extremely loyal to his pack and to the person he loves. For example, in many stories, he'll go to great lengths to protect his love interest from any danger, whether it's from other supernatural beings or just regular human problems.
One way is to make time - travel related to the sea currents in One Piece. Since the sea currents are already a unique aspect of the world. For instance, there could be a special sea current that appears once every hundred years and can take a ship to a different time period. But there are risks involved, like the ship might get lost in a time rift if the journey isn't timed correctly. Writers can also tie time - travel to the ancient poneglyphs. If a certain combination of poneglyphs is deciphered, it could open a time - travel gateway, but only those with a special connection to the Void Century can activate it.