Maybe the time machine in the fanfic allows Harry to travel to different points in wizarding history. He could end up in the time of the founders of Hogwarts. There, he learns secrets about the four houses that were long forgotten. He might also get involved in the early battles against dark wizards, and bring back some ancient spells or knowledge that helps him in his fight against Voldemort in his own time.
In this fanfic, the time machine could malfunction and send Harry to random time periods. He first lands in a time when wizards were being hunted by muggles. He has to figure out how to survive and get back to his own time. Along the way, he meets a young wizard who is the ancestor of one of his friends. He tries to help this young wizard, and in doing so, changes the family's fate which has a ripple effect on his present - day friend.
Well, in a 'Harry Potter Fertility Machine Fanfic', it could be that some wizard or witch invents this strange fertility machine. It might be set in Hogwarts or in the wizarding world at large. Maybe it's a story where Harry and Ginny are having trouble having a baby and this machine becomes a part of their journey to start a family. Or it could be about some other characters like Hermione and Ron dealing with similar family - starting challenges and the machine plays a role in their story.
A great plot twist could be related to the time - travel itself. What if the way time - travel works in the WW2 era is different from how it is in Harry's time? This could lead to him getting stuck or being unable to use his magic properly. Or perhaps he discovers that a certain event in WW2 was actually caused by a wizard from the future (not just him) who was trying to correct something in the wizarding world's past. His attempts to fix things could then make the situation even more complicated as he unknowingly steps on the toes of a much larger time - traveling plan.
Harry would be excited at first. He's always been curious about the past, especially about his parents. Hermione would be cautious. She'd worry about the implications of changing time and would constantly remind Harry of the dangers. Ron would be a bit more laid - back, but also eager to see what they could do with the time machine. For example, he might want to go back to see a famous Quidditch match in the past.
Perhaps in the fanfic, Amelia Bones discovers a time - traveling device. She decides to go back in time to save her family members who were killed by Death Eaters. In the past, she meets Harry Potter's parents, Lily and James. They become friends and work together to fight against the early threats of Voldemort. When she returns to her own time, she has new knowledge and power that she gained from the past. This changes her perspective and makes her a more formidable force in the fight against the remaining Death Eaters in her own time.
The plot could be that Harry, while exploring the Forbidden Forest, stumbles upon a time - traveling portal and is transported to a time when sand phoenixes roamed freely. He befriends a young sand phoenix and realizes that it is being hunted by an evil sorcerer. Harry decides to protect the sand phoenix and in the process, discovers a way to use the sand phoenix's time - warping abilities to fix some of the past mistakes in the wizarding world.
The fanfic could center around Harry's life outside of the main events of the books. For example, it could explore his summer holidays in more detail. He could be spending time in the Muggle world and using his magic in creative ways to solve normal, everyday problems. He might use magic to help his neighbor fix a broken fence without the neighbor realizing it was magic. This would add a new dimension to his character and show how he can adapt his magical abilities to different situations.
Well, the plot might involve them facing a threat that only their combined skills can defeat. Harry Potter is good at spells and dealing with magical creatures, and The Doctor is a time - traveling genius. So they could be fighting an enemy that has the ability to manipulate time in the wizarding world, something that neither of them can handle alone. Harry could use his invisibility cloak to sneak around while The Doctor figures out the science behind the time - manipulation.
Well, it could be about Harry Potter somehow getting involved with the power of the God of Destruction. Maybe he accidentally stumbles upon an ancient artifact that has the essence of the God of Destruction. This could lead to him having to control this new and dangerous power while still dealing with the threats in the wizarding world, like Voldemort or other dark forces.
Well, in a Harry Potter pneumonia fanfic, it could start with Harry being cursed by a new dark spell that gives him pneumonia as a side - effect. As he struggles with the illness, he starts having strange visions. These visions could be related to Voldemort's past or some hidden secrets in Hogwarts. Ginny, being worried about Harry, decides to take matters into her own hands and teams up with Neville to find a way to break the curse and cure the pneumonia. The story could be full of mystery and adventure as they explore the unknown parts of the castle for a cure.
Well, perhaps in the fanfic, the wisdom teeth could be enchanted. Maybe they start to give Harry the ability to speak Parseltongue even better, or they could be a key to unlocking some hidden magic within him. But this new power also attracts unwanted attention from the wrong sort of wizards. So, Harry has to figure out how to control this new development while dealing with the pain of his wisdom teeth.