Luke castellan was the older brother everyone wanted. Most people at camp half-blood saw him as the older brother, I mean, he was the "golden boy". You were just lucky enough to have him as your brother. Luke and you ran away from home when you were around five, and he was fourteen. Your mother, May, had been the Oracle. Sadly, she went crazy after your father, Hermes. She found out Luke's written prophecy, and couldn't handle it.
Life at camp wasn't horrible. You had a bed, good, training options. It was the closest thing until perfect. Until Percy Jackson appeared at camp. He was new, he went on a quest for the lightning bolt. The night he got back, Luke had pulled the blankets a little higher. Luke had kissed your forehead that night, then left the cabin to "celebrate the quest".
The next morning, Chiron was visiting you. Luke wasn't there, he had left. He joined Kronos. In percys words "he betrayed camp". Not Luke, not your dear older brother Luke. He hadn't said goodbye, but the way he hugged you a little tighter when you requested that he told you a bedtime story should've been a hint. Luke stole zeus' bolt, for Kronos. Luke Castellan, the leader of the titans army.
It's been years, and oh how dearly you missed your brother. Camps golden boy, now dying slow from Kronos. The hero he could've been, the future. You always thought that maybe one day, Luke would walk you down the wedding aisle. Maybe one day, in another life, he did.
It's the battle of Manhattan. So many campers have fallen, the minotaurs from Kronos army wore the fallen children's camp necklaces with pride, showing the way they slaughtered the young demi-gods. It was going fifty-fifty. Then Luke turned up with a whole new heap of demi-gods that had joined him, you never got a choice.
It came to the point where Kronos was winning. Luke searched the fields, his now golden, once brown, eyes searching. You. Fighting, just like him. Only, the opposite side of the war. Luke hadn't seen you in a long while, as he had betray you, his little sister. The only way for Kronos to disappear completely, was for the vessel, to die.
The metal of the sword dug through Luke's Achilles spot, the weakest spot in a demi-gods body that causes basically instant death. Luke was the body vessel of Kronos, and he needed this war to end. All that work, all the betrayal, just for his life to end with a sacrifice to the one's he fought.
The battle stopped, and the bodies were taken away. Percy came to your cabin, his head hung low, as a result of mourning for all the lives lost. His knock echoed the wood a few times, the usual loudness of the full hermes cabin, now quiet with remembrance. Percy knew you went there after the battle, Percy also knew that you didn't have a clue on how they won.
Percy glances towards the lake, where a burial shroud was holding Luke Castellan, the fallen son of Hermes. He had to break the news to you thst Luke had died, no matter the betrayal, it would hurt knowing he had passed. You deserved the goodbye you never got.