It had started when he was still very small. Natsu had never really been able to get really close to anyone because of what had happened in his past. He loved Igneel, Igneel left him and died when he finally found him again. The Old Woman that had raised him when Igneel had left him, put him on a train to Magnolia to join a mage guild and when he wanted to visit her again he learned that she had died years ago. Gildarts, left him. Lisanna, died...
Eventually he had just given up on getting close to people. The only 'person' he still allowed himself to be close to was Happy; the blue exceed always had his back when he needed it the most and knew everything about him. He was the only one that knew about Natsu's fear of letting himself get close to people and how that fear had only gotten worse after he had learned that he was E.N.D and that Zeref, who was in possession of the book of E.N.D could let him transform into a monstrous demon that would kill everyone he had ever known.
After that last encounter with Zeref, Natsu had just kinda locked himself inside of his own little world. He would still act normal against other people though. They didn't know he was a terrible demon deep inside that could transform at any given moment if Zeref felt like it and kill everyone around him. They would only question him when he would openly distance himself because that just wasn't Natsu-like.
But once he was alone, or alone with Happy. He would distance himself in his room; sitting on his bed in foetal position and slowly rocking himself back and forth. Sometimes Happy would snuggle up against him to comfort him when he was having a really hard time. But he mostly let Natsu be when he was like this because he knew that Natsu needed time to process all of this and maybe he would ever be the normal, cheerful Natsu again he once had been.
There had been once that Natsu felt something was really wrong and he had told Happy to lock him inside their house and go to the guild. When Happy returned two days later because he hadn't heard of Natsu in the meantime, there were scratch marks on the walls everywhere and several pieces of interior were burned. When he had asked Natsu what was wrong, he had answered him "It happened Happy. I transformed into E.N.D that evening."
After what had happened that night, Natsu started openly distance himself too. Many of their friends started worrying about their friend but when they went to check on him, he just growled at them that they needed to stay away from him and send them back to where they came from. After a while, they just stopped trying to communicate with him and let him be on his own if that was what he wanted, hoping that one day the normal, cheerful Natsu they had always known would return like nothing had ever happened.
Right now Natsu was sitting at the little grave he had built in his backyard. The only 'person' he had ever allowed him to get close to had died two years ago. Natsu was all alone now. No one understood him, no one knew what he really was and how dangerous he could be. No one except for Happy.
But Happy wasn't here anymore...
