Rise from the Ash: Book One

When Mewtwo and Mew clashed, Ash died. When their tears and wish brought them back, Ash lived. But when the wish, granted by Jirachi, is "Don't die, Ash!" Ash doesn't die. He doesn't age, and the world dies around him. His natural luck was simply his immortality, and his agelessness a curse. Rescued by the Legendaries from his pain, in time they decide to set off to a new world.