I think it might be Nico. Given his experiences with different types of beings in his own world, he might sense the supernatural nature of the Winchesters and approach them first, either out of curiosity or because he thinks they could be allies in his ongoing battles against the forces of the underworld.
It could also be James. James is a natural leader and is always looking to include interesting people in his circle. When he sees Nico, he might sense that there's something special about him. He'd probably start by asking Nico about his abilities and before long, they'd be chatting like old friends. Plus, James has a big heart and would be accepting of Nico quite quickly.
Another storyline could involve Nico being on a quest in his own world, but it somehow intersects with Gotham. For instance, a powerful magical item has been stolen and ends up in Gotham. Nico follows it there and meets Batman. At first, they don't see eye to eye as they have different methods. But as they face challenges together, such as fighting off the villains who also want the item, they start to understand and trust each other more. This could lead to a long - term friendship or at least an alliance where they help each other out in future situations.
One possibility is that Nico, with his powers over the dead, could really freak out Batman at first. Batman is used to dealing with normal criminals and the occasional super - villain with scientific powers. Nico's dark and otherworldly abilities would be something completely new to him. Maybe Nico would mistake Batman for some sort of undead creature at first because of his all - black costume and brooding nature.
In the fanfiction, Nico might find himself in some of the Marauders' pranks. Since the Marauders are known for their mischief, they could include Nico in one of their elaborate schemes against the Slytherins. Nico, being from a different background, might have a different perspective on these pranks and could either enhance them or try to stop them depending on his moral compass at that moment.
Well, if Nico di Angelo meets Voldemort in a fanfiction, it depends on the writer's take. Nico could see Voldemort as just another evil entity to oppose. He might use his connection to the Underworld to his advantage. For example, he could summon some undead creatures to fight against Voldemort's Death Eaters. Voldemort, on the other hand, would probably view Nico as a strange and unexpected foe. He might try to use the Killing Curse on Nico, but Nico's ability to disappear into shadows could make it difficult for Voldemort to land a hit.
Well, Nico could use his powers to surprise the Avengers. Maybe his shadow - traveling ability would come in handy during a battle, like he could quickly transport himself and some Avengers to strategic locations.
One potential conflict could be their different views on power. Captain America believes in using power responsibly for the good of all, while Nico has powers that are often associated with death and the underworld. This might make Captain America a bit skeptical of Nico at first.
In a fanfiction scenario, Nico di Angelo and Captain America could team up. Nico could use his shadow - traveling abilities to get them out of tight spots. Captain America would bring his leadership and combat skills to the table. Their meeting might also lead to some interesting cultural exchanges, as Nico comes from a world of Greek mythology and Captain America from a more modern, American - military background.
One common theme is the clash and subsequent melding of different mythologies. Since Nico comes from Greek mythology and Magnus from Norse, there's often exploration of how these two very different mythological systems interact. For example, how their respective magic or powers work in relation to each other.