Well, in a lot of these fanfictions, Hades might be overprotective in terms of Nico's social interactions. For example, if Nico wants to make new friends among the demigods, Hades might be hesitant and try to limit it. He could be worried that Nico will get hurt either physically or emotionally. Also, when it comes to Nico's training or using his powers, Hades might be overly cautious and not let him push his limits as much as Nico wants to, fearing that he could lose control or get injured in the process.
One common theme is friendship. Percy's overprotectiveness can be seen as an extreme form of his friendship with Nico. He wants to keep Nico safe from the various threats in their world, which shows how much he values their bond.
Well, without actually reading the fanfiction in question, it's difficult to say exactly. It could be that the author is exploring a darker side of the relationship between Nico and Hades, perhaps for the sake of creating drama or exploring certain themes like power imbalance or trauma. Fanfictions often take existing characters and put them in new and sometimes challenging situations.
One place to start looking could be Archive of Our Own (AO3). Just search for 'percy is overprotective of nico' in their search bar, and you'll likely find a good number of relevant fanfictions.
Another theme is the exploration of the Underworld. Given Hades' domain, many 'baby nico and hades fanfiction' stories take the opportunity to describe the Underworld in detail, with Nico being the newcomer and learning about this strange place. It can be about the different regions, the creatures there, and the rules that govern the Underworld.
Finding such a specific fanfiction can be tricky. You could start by looking on popular fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. But keep in mind that content related to abuse might be restricted or tagged appropriately on these sites.
You should definitely check AO3 first. It has a well - organized tagging system that makes it easy to find what you're looking for. If you don't find enough there, you can also look at some independent fanfiction blogs. These blogs often focus on specific fandoms and might have some unique 'Hades and Nico cuddle' fanfictions that haven't been widely shared elsewhere. Another option is to join relevant Facebook groups dedicated to the fandom and ask for recommendations.
One interesting story could be about Hades teaching Baby Nico about the Underworld in a gentle way. For example, showing him the different regions like Elysium and the Fields of Punishment in a way that a baby could understand, like through simple pictures made of shadows.
You can try fanfiction websites like Archive of Our Own. It has a large collection of fanfictions on various topics, including Hades and Baby Nico. Just use the search bar and type in relevant keywords to find the stories you like.