Perhaps he was poisoned. Given the dangerous situations he often gets into, someone could have slipped a poison into his food or drink. It might be a poison that is designed to specifically target demigods like him. Or, it could be related to his heritage. Since he is a demigod, there could be some genetic factor that makes him more susceptible to certain types of sickness, and in the fanfiction, this could be explored as he gets sick.
In the fanfiction, one possible cause could be that he ate some bad leaves. Maybe the leaves were contaminated with some kind of toxin from a nearby factory. Another cause could be that he caught a strange virus from an animal that recently visited the zoo.
It could be a magically - induced illness. If there are magical forces at play in the fanfiction world, an evil sorcerer or a cursed object might be the culprit. For example, he might have unknowingly touched a cursed amulet that started draining his life force, leading to him getting sick.
Well, in the Chronicles of Narnia, Lucy could get sick perhaps due to the magic of Narnia going awry. Maybe she was exposed to some dark magic or a spell that made her ill. Another possibility is that she ate something in Narnia that her human body couldn't tolerate. For example, some strange Narnian fruits or plants that had an unexpected effect on her.
Well, it could be a werewolf - related illness. Maybe he was bitten by a strange creature in the woods that carried a new virus or something. Another possibility is that some kind of magic or spell has been cast on him, making him sick as part of a bigger plot.
In this fanfiction, it might be due to his poor living conditions. He doesn't always have the best food or a warm, clean place to stay. His body could be weakened from not getting enough nutrition, which makes him more likely to get sick. Also, the emotional turmoil he goes through with losing friends and dealing with the Socs could take a toll on his immune system.
One possible plot could be that they discover they are long - lost relatives through some sort of mystery. Maybe there's a hidden family connection that gets uncovered as they both work on a big project together.
I don't think the gods read Leo Valdez fanfiction. Gods in that universe are often busy with more important things. They have to manage their powers, deal with other gods, and look after the affairs of the demigods. Fanfiction is a form of human creativity, and it's not something that would likely be on the gods' radar. It's more of an entertainment for the fans of the Leo Valdez stories.
Perhaps in the fanfiction, Tobirama's sickness makes him weak and he starts to reflect on his life and the choices he has made. He could have conversations with his loved ones where he reveals his regrets or hopes. This introspective side of him due to the sickness could add depth to his character. Also, his sickness might be a catalyst for changes in the village he has helped build, as others step up in his absence.
Well, it could start with Leo being his usual witty self and catching the eye of a girl. Maybe they meet at Camp Half - Blood during a quest preparation. Leo, with his mechanical skills, might create something special for her, like a unique piece of jewelry that has some magical properties. Their relationship could grow as they face challenges together, like fighting off monsters. He'd use his fire - starting abilities to protect her, and over time, their love would blossom as they discover more about each other.
The fanfiction could explore Leo's relationship with Tony Stark. Leo might be rebellious at first, not wanting to follow Stark's strict rules. But as they face challenges together, like an alien invasion or a powerful supervillain, they grow closer. Leo could introduce Stark to his friends from the Percy Jackson world, and they all team up to save the world. There could be a lot of humorous moments as the two different universes collide, and Leo tries to make sense of Stark's high - tech gadgets while Stark is baffled by Leo's magic.