By limiting the time. If a Pokemon has only a short amount of time to be saved, it creates immediate tension. For example, if a Pokemon is poisoned and will die in an hour if not treated.
One example could be a story where a Pokemon is poisoned in a battle and reaches a critical condition. The trainer then has to race against time to find an antidote. Another could be a Pokemon getting seriously injured while protecting its trainer from a powerful enemy Pokemon.
Another way is by showing the desperation of the characters trying to rescue the kidnapped one. If they face numerous obstacles like powerful enemies or difficult terrains, it adds to the tension. For instance, if the Cullens have to fight through an army of new vampires to reach the kidnapped character, the readers will be worried about their success.
The main reason authors do this is to add drama and suspense. It builds anticipation and makes the reader emotionally invested in the outcome. Also, tension helps drive the plot forward and makes the story more memorable.
Another way is through the slow development of the relationship. The captor may start off as cold and distant, but as they interact more with the captive, small changes occur. This slow burn while the captive is still in a kidnapped state keeps the reader on edge, wondering when and how the relationship will fully develop into a romantic one.
By introducing dangerous enemies. In these fanfictions, there could be new, more menacing villains than in the original series. The threat these villains pose to Harry and Hermione, and their plans, keeps the readers on the edge of their seats.
Authors often create tension through the initial reluctance of the characters. For example, if one character is against the idea of an arranged marriage, there will be conflict. Another way is by introducing external factors like family expectations or cultural differences. This can put pressure on the relationship and create tension.
One way is through the power dynamics. For example, if the male lead is a powerful mob figure and the female lead is an ordinary person, the difference in their status creates immediate tension. He has the power to control her situation, which makes their relationship precarious.
It could be a rogue ninja from another village who has a vendetta against Konoha. This ninja might have a special ability to target Naruto specifically and put him in a critical state.
Authors create tension by showing the villain's near - successes. When the villain is almost about to achieve their evil goal, like taking over the world or destroying the hero, it makes the readers nervous. For example, if a villain is just one step away from activating a doomsday device, the readers will be on the edge of their seats. Another way is by making the heroes' situation seem dire. If the heroes are outnumbered or outmatched by the villain's forces, it creates tension as the readers wonder how they will overcome the odds.
Authors often combine different Pokemon types or features. For example, they might create a Pokemon that has the body of a water - type but the wings of a flying - type. Another way is by giving new abilities to existing Pokemon. They can also create new evolutionary lines for known Pokemon. This gives a fresh take on the familiar Pokemon world.