Well, perhaps Percy shows up at his own funeral in the fanfiction because he wasn't really dead. He might be confused as to why everyone thought he was gone and start revealing secrets that change everyone's perception of his 'death'.
His friends could be involved, like Annabeth. She might be mourning at the funeral and then be extremely surprised and happy when Percy shows up. Grover could also be there, and he'd probably be the first to give Percy a big, emotional hug.
Some characters might react by changing their own identities. For instance, one of Percy's friends who was always a bit of a follower could become a leader, inspired by Percy's leadership. They could start leading quests in a way that Percy would have approved. The gods could also react uniquely. Instead of just mourning, they could grant Percy posthumous honors. Zeus might name a constellation after Percy, and Poseidon could make a special underwater grotto dedicated to him, filled with all the things Percy loved during his life.
One heart - wrenching scene could be when his friends gather around his body. Annabeth might be holding his hand, tears streaming down her face as she recalls all their adventures together. Another could be when his demigod powers seem to flicker one last time, causing a soft glow around him, as if his spirit is trying to hold on. And perhaps the sea itself, which Percy has such a connection to, becomes unusually calm and still, as if mourning his loss.
Grover could be a popular character. Since he's Percy's best friend, he might be involved in the fanfiction, perhaps helping Percy protect his mom or going on adventures with them. Another could be Annabeth. Her intelligence and skills could be useful in the stories, like when they are facing a difficult situation and she comes up with a clever plan.
The story behind 'Lightning Crashes' is somewhat ambiguous and open to interpretation. It could be seen as a metaphor for the unpredictable nature of life and how even in the midst of chaos, there can be hope and renewal.
In the fanfiction, Percy could start by reaching out to his friends. They might offer him support and understanding, which could be a great help in dealing with his depression.
Once upon a time in Equestria, there was a beloved MLP OC named Starlight Glimmer. She was known for her kind heart and beautiful mane. But one fateful day, she passed away. Her friends gathered for the funeral. Pinkie Pie tried to keep the mood light with some songs, but everypony was still deeply sad. Twilight Sparkle gave a touching speech about how Starlight had changed their lives. The whole place was filled with sorrow as they said their final goodbyes to Starlight Glimmer.