Well, in fanfiction, there could be several reasons. It could be that Nico is suffering from some sort of after - effect of a battle. Maybe he was exposed to a harmful spell during combat and now his body is trying to expel the negative energy. Another possibility is that he's feeling homesick for the underworld in a way that his body rebels against the surface world, causing him to feel ill and throw up. Or perhaps he's caught a strange disease that is affecting demigods, and the first symptom is vomiting. And, of course, there could be some sort of emotional turmoil related to his relationship with Will that is so intense it makes him physically sick.
There might not be a whole lot of fanfiction specifically focused on 'Nico throws up' within the Solangelo context. However, if you dig deeper into the Solangelo tag on fanfiction sites, you may find some stories where Nico experiences some sort of distress that could potentially lead to such a situation. For example, a story where he's been poisoned or is extremely ill due to some magical affliction. But it's really going to take some time to sift through the available works.
Well, one possible plot could be that the other characters in the Solangelo universe are super confused at first. Percy might be all like 'Whoa, a baby Nico?'. They'd have to figure out how to take care of him. Maybe Will is the most determined to find a way to turn him back and in the process, there are some really cute and funny moments like baby Nico trying to grab Will's stethoscope and put it in his mouth.
One possible reason could be that their different career paths put a strain on their relationship. Ron might be more focused on his Auror work, often away on dangerous missions, while Hermione is deeply involved in the Ministry's research and reform projects. The long hours and high - stress of their jobs could lead to less time for each other and growing apart.
Well, perhaps Percy has some personality traits that don't mesh with what Nico is attracted to. Maybe Percy is too outgoing and boisterous for Nico, who might prefer someone more reserved.
One possible reason is that their personalities clash. Percy is often portrayed as a more outgoing and confident character, while Nico is more introverted and brooding. In a fanfic, this could lead to misunderstandings and animosity between them. For instance, Percy's bold actions might seem reckless to Nico, causing him to dislike Percy.
Maybe the loss of a very dear Pokémon friend. If something bad happened to a Pokémon he was extremely close to, like it getting seriously injured or lost forever, it could be so devastating that he loses the will to continue his journey and thus gives up.
Perhaps the fanfiction keeps rehashing the same tired storylines about Konoha. Naruto might be tired of seeing the same things over and over again, like always focusing on the village's dark secrets in a clichéd way instead of exploring new aspects of Konoha and its people.
One possible reason could be the overwhelming loss he has faced. He's lost many dear friends and mentors throughout his journey. For example, when Jiraiya died, it was a huge blow to him. Another reason might be the constant pressure of being the savior of the village. The weight of everyone's expectations could lead him to feel so tired and defeated that he gives up on life.
One possible reason could be differences in their future goals. Naruto is highly focused on being Hokage and protecting the village, while Hinata might want a more peaceful, family - centered life. Maybe Naruto's hectic schedule and constant danger make Hinata feel neglected, leading to their break - up.
One possible reason could be that Naruto realizes Sasuke is too far gone on his dark path. After numerous attempts to bring him back, Naruto might start to think that Sasuke doesn't want to be saved. He may see that Sasuke's actions are causing too much harm to the village and the people he loves, and Naruto has to prioritize them over Sasuke. So, he gives up on the idea of bringing Sasuke back.