There's a fanfiction titled 'Hidden Tears'. Here, Percy is crying because he misses his mother deeply. Nico, while on one of his solitary walks around the camp, finds Percy in the forest. Nico is surprised as Percy usually seems so strong, but he stays with Percy until he calms down.
One possible fanfiction could be 'The Unseen Pain'. In this story, Percy might be crying due to the overwhelming pressure of his demigod duties. Nico stumbles upon him in a secluded corner of Camp Half - Blood. Nico, initially hesitant, decides to approach Percy and offer his silent support.
In a fanfiction called 'When Walls Break', Percy is crying because he feels alone despite all his friends. He's been through so much and it all just hits him at once. Nico discovers him crying in his cabin. Nico, who has also felt alone at times, understands Percy's pain and tries to comfort him with stories of his own struggles.
Fanfiction.net is also a good place. Just use the search bar and type in key words related to the scenario, like 'nico', 'percy' and 'crying'. There are likely to be some stories there.
I don't think it's a very common or popular theme. The Percy Jackson fandom usually focuses more on positive relationships and adventures among the characters. Choking is a rather dark and extreme concept that doesn't really fit the general tone of the fandom most of the time.
Perhaps he's feeling guilty about something that happened during one of his quests. Maybe he made a decision that had negative consequences for someone he cares about, and that's weighing on him. It could also be that he's just had a really tough encounter with a powerful enemy and is letting out the pent - up stress and fear through crying.
Well, in some versions, Percy might be initially shocked. He could be like 'Whoa, I had no idea!'. Then he might start to see Nico in a new light, with more understanding and compassion.
Nico might be initially shocked. He could feel a deep sense of anger towards whoever was responsible for Percy's abuse. Then he would probably become very protective of Percy, vowing to keep him safe from any further harm.
I'm not sure where you can specifically find a fanfiction with that exact plot. You could try popular fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. Just search for relevant tags like 'Percy', 'Nico', and 'Will' to see if such a story exists.
One possible plot development could be Nico seeking justice for Percy. He might start to investigate the abuse on his own and gather evidence against the abuser.
The camp leaders might betray them. If there is a power struggle within the camp, and Percy and Nico are seen as threats to the current leadership's power, the leaders could set them up. They could make it look like Percy and Nico are breaking camp rules or endangering the other campers, which would lead to the rest of the camp turning against them.
One common plot twist is that Percy actually realizes he has feelings for Nico too, but he's been suppressing them. It's like a sudden realization that hits him when he finds out Nico likes him.
Yes, there are many. You can look for ones on platforms like FanFiction.net. Just search for 'Percy and Nico friendship' and you'll find a lot of great stories that focus on their bond as friends, like adventures they might go on together or how they support each other in the face of challenges.