It could be some remaining monsters that survived the giant war and are now seeking revenge. They might target Nico specifically because of his role in the war. Another possibility is some rogue demigods who didn't like the outcome of the war and blame Nico for it.
Another option could be a new demigod. A character who was not very involved in the war but is now thrust into the post - war chaos. This new character could bring a fresh perspective and could be learning about the demigod world and its history while also trying to help in the rebuilding and healing process.
Some former Death Eaters who escaped justice could be the main antagonists. They might be plotting to bring back Voldemort's ideology in a more covert way. Another possibility could be new dark wizards who emerge, seeing the post - war chaos as an opportunity to gain power.
Well, one possibility could be Nico dealing with the aftermath of the war. Maybe he's trying to find his place among the survivors. He might be struggling with PTSD from the battles he faced. Another could be him forming new relationships or strengthening old ones. For example, he could become closer to his friends from Camp Half - Blood.
There's a possibility that it's a new character introduced in the fanfiction. This new character could be someone who has a connection to the events of the giant war, like a relative of a fallen hero. They might be exploring the post - war world, uncovering secrets that were hidden during the war, and their journey could be the main focus of the story.
It could be some rogue ninjas who were against the peace treaties after the war. They might form a group and try to disrupt the newly - established peace in the ninja world.
Nico di Angelo could be a main character as well. His powers over the dead and his unique perspective could be valuable. He might be dealing with the influx of new ghosts due to the large number of casualties in the war and trying to find a way to give them peace.
Another option for antagonists could be a new organization that rises in the power vacuum left after the war. They might have different ideologies from Naruino and his village. For example, they could believe in total domination rather than the peace and co - existence that Naruino stands for. They would see Naruino as a threat to their plans and try to eliminate him.
It could be a rogue demigod who was on the losing side of the Giant War and is now seeking revenge. This demigod might have found some dark power or be allied with some minor but dangerous mythical creatures.
The healer could be an old, wise wizard. Wizards are often depicted as having great knowledge and magical abilities in many fictional universes. This wizard could have seen the horrors of the war and decided to use his powers to heal those in need, like Nico.
Some of the pure - blood supremacist families who still hold grudges against Harry could be antagonists. They might not approve of Daphne getting involved with Harry, seeing him as a threat to their traditional values. For example, some of Daphne's extended family members who are still stuck in the old ways could try to break them up.