Her best friend could be in it. This friend might be the one who first notices that Lucy has a fever and takes her to the doctor or calls for help. And perhaps there's a love interest, who shows extra concern and brings her flowers or little gifts to cheer her up while she's sick.
There could be her family members. Her mother might be the one constantly checking on her temperature and making sure she is comfortable.
Maybe it could be about how her friends take care of her. They might bring her medicine, make her soup, and stay by her side to comfort her while she's dealing with the fever.
One possible motive could be revenge. Another character might have a grudge against Lucy for something she did in the fictional world, like betraying a group or stealing something precious.
Obviously, Lucy is one of the main characters since the fanfiction is centered around her getting burned. There might also be characters like her family members, such as her parents or siblings, who could play important roles in her recovery process.
One possible plot could be that Lucy trains intensively with Natsu by her side for support. They might go on special quests to find magical items or training methods that can enhance Lucy's power. For example, they could search for an ancient spell book that has the power to unlock new celestial spirit powers for Lucy.
The main characters are clearly Natsu and Lucy. Natsu, with his fiery and impulsive nature, is likely to be there to encourage and sometimes push Lucy in her journey to get stronger. His dragon slayer magic might also play a role in training her or protecting her during dangerous situations.
She might use her celestial spirits in unexpected ways against the guild. For example, she could have her spirits create illusions to embarrass the members.
Gray's character development could be quite significant. He might start to show his softer side more often. Usually, he's all about the ice - cold exterior, but now he has to think about a family. He could become more of a family man, putting Lucy and the baby's needs above his own. For Lucy, she'd grow in confidence. She'd have to be strong for the baby, and this would make her more assertive in the guild. She might also start to take on different roles, like teaching the younger members about family values that she's learning herself.
In the 'ichigo gets a fever fanfiction', it could start with Ichigo suddenly feeling unwell and getting a high fever. His family might be in a panic. His father, being a doctor, would first examine him. Meanwhile, his friends from the Soul Society could sense his weakened state through their spiritual connection and try to find a way to help him. This could lead to a series of events where they have to face challenges both in the human world and the Soul Society to get the right remedy for Ichigo.
Ross would be extremely worried. He would likely call for the doctor right away and stay by Demelza's side, constantly checking on her temperature and making sure she was comfortable.
Lucy could face isolation. People in the fanfiction world might avoid her, and she could be left all alone. This could also lead to her losing confidence in herself as she is constantly being blamed for something she didn't do.