The vast majority of ninja, Kakashi included, are atheists. It's almost an occupational hazard, or a part of the job description that they don't mention in the Academy.
This is what makes a ninja, Kakashi thinks, blood and bone, skill and steel, and a lack of faith.
Although, like most of what Kakashi tells himself, that isn't exactly true. It's not the how much faith he has, or how little, but rather where he chooses to place it that matters.
Kakashi has faith in himself, in his skills and his wits and the eye that Obito gave him. He has faith in the voices that whisper to him: the louder ones that tell him of things he can't forget, and the quieter ones that hiss and whisper of the things he doesn't want to remember. It they speak in voices not his own, that's alright, he has faith enough in their sanity, if not his own. He has faith in his nin-dogs and faith in their faith in him. He has faith in the lessons his teachers taught him; not just the jutsu and the fighting forms, but the more important ones, the ones that really mattered.
For all of that, though, there are places where Kakashi has lost faith, places like little holes etched inside of him that the wind blows through, or the rain on stormy days.
Kakashi had faith in his father, when he was young, when he was younger than he can really remember anymore. Faith in the man's skill, in the comfort of the man's shadow, of how tall the man stood, how proud. That faith died when Konoha's White Fang did, gutted on his own blade, blood spreading out and creating shapes that would stain into the wood of the floor and stayed even after they moved the body away, cleaned up as best they could. Strange shapes, the lifespan of his father, that death impressed into the wooden floors of his family's home.
Kakashi had faith in his team, in the ability of others to carry through the mission, but Obito's crushed body and blood-flecked words stole most of that from him, and the theft was completed by the soft sound Rin made - surprise almost, or maybe fear - when she stumbled backwards, hands too slick with blood to hold the pieces of her stomach together, intestines trailing out like the necklaces he'd never seen her wear. They'd pieced together enough of her to bury, although no body lies beneath Obito's gravestone. In ANBU, Kakashi was a solo operative; deadly, efficient, and so very cold.
Kakashi had faith in his teacher, in the Yondaime's fierce ability that was always so at odds with his kind smile, but on that night, when the Kyuubi's snarls split the air and the ground shook, his teacher had smiled as he ruffled Kakashi's hair. Smiled that same smile, and his eyes were so sad as he looked down at his son, look down at the mangled form of his wife. He had looked at Kakashi when he walked past him, looked and smiled and ruffled his hair and gone to die. There had been no mark on his body, but although Kakashi was a good liar, he was a better ninja and knew too well what death looked like.
He had faith in change, and maybe he still does, as small and frail as it is, but he feels that disappearing as well, slipping away from him whenever Naruto smiles, the expression paired with a determination so familiar that it hurts to watch. A faith that fades when Sasuke leaves, a dark boy following a darker destiny and he's too late to help, too late to change anything. Sakura takes to Tsunade's training with a skill she never used but he knew she had, and heaven, hell, god, whoever's listening or caring, he doesn't want to watch this happen all over again.
Perhaps Kakashi had faith in a god once; once, when he was still young enough to try. But it's been too long, and he's put his faith and lost his faith in too many things since then. There's no room for a god or gods, no space left and he has nothing left to give.
But he wants to believe, he thinks as he stands by the monument and the rising sun traces over names he knows as well as his own. Wants to place that faith, however foolish it might be, for reasons as selfish as they are unselfish: for the hope that they're in a place better than this one, and the hope that one day he may see them again.