In some 'sans gets sick fanfiction', the plotline could be centered around Sans' internal struggle while being sick. He might be used to being strong and independent, and now that he's sick, he has to deal with feelings of weakness and vulnerability. His friends and family's attempts to help him could also be a major part of the story, showing how much they care for him and how they all grow closer through this difficult time.
One plotline could be how the other characters in the story react to Sans being sick. For example, Papyrus might be overly worried and try all sorts of crazy remedies. Another could be Sans trying to hide his sickness because he doesn't want to be a burden.
A plotline might involve Sans' sickness being some sort of strange magical ailment that no one really understands. So the whole community has to come together to figure out what's wrong and how to cure it. This could lead to all kinds of adventures and character interactions.
Alphys could be another common character. As the royal scientist, she might be called upon to figure out what's wrong with Sans. She could bring her scientific knowledge to the table, trying to diagnose and find a cure. Her own insecurities might play a role here too, as she might be worried about failing to help Sans.
One possible plotline could be that while Ash is sick, his Pokémon have to take care of him. Pikachu might gather berries to make a special potion to help Ash get better. Another could be that Ash's friends are on a journey without him because he's too sick to travel, and they constantly worry about him and send back items to help his recovery.
In this type of fanfiction, a plotline could be that Ichigo's sickness is caused by some sort of spiritual poison or curse. His friends then have to go on a quest to find the antidote. It could involve a lot of detective - like work, like figuring out who poisoned him and why. Another aspect could be that Ichigo's sick state makes him more vulnerable to his inner demons. He might have hallucinations of past failures or enemies, and he has to fight them off mentally while also dealing with his physical illness.
One interesting Sick Sans fanfiction could be about his unique battles. In some stories, he uses his special powers in very creative ways against his foes. For example, he might manipulate the environment in ways that are both unexpected and fascinating.
One possible plotline could be Danny trying to hide his sickness from his enemies while still fighting ghosts. He might be weaker than usual, but his determination keeps him going.
One possible plotline could be Harry realizing his feelings for Tom while they are forced to work together on a difficult magical task. Another could be Tom's internal struggle between his dark ambitions and his growing love for Harry. A third might be a scenario where they are transported to an alternate dimension and have to rely on each other to get back, during which their love develops.
One possible plot could be that Batman gets a mysterious illness that not even the Batcave's high - tech medical equipment can diagnose. As he gets weaker, Gotham's criminals start to become bolder. The Bat - family has to work overtime to keep the city in check while also trying to find a cure for Batman.
One plot could be Naruto getting a mysterious illness that no one in the village can figure out. His friends, like Sakura and Sasuke, start to search for a cure. They might go on a journey to find a rare herb or seek the help of an old sage. Another could be that the illness is a result of a new enemy's jutsu. As he gets sicker, the village starts to worry about their future without their hero.
One possible plot could be that Naruto's friends have to take on his missions while he is sick. They struggle at first because they realize how much Naruto usually does. Another could be that Naruto tries to hide his sickness from everyone, but his body keeps giving him away, like fainting during training. And a third plot might be that a new enemy takes advantage of Naruto's weakened state to attack the village.
Well, a plotline could involve Inuyasha's pregnancy being a result of some magical or otherworldly event. This could lead to a search for a way to reverse it or accept it. Also, his pregnancy might bring out a more nurturing side of his personality that was previously hidden. He could start to bond more with characters like Kagome in a different way as they support him through this strange situation.