Perhaps there's a plot where a powerful ninja in the Naruto universe is experimenting with dark magic and accidentally opens a portal to the Left 4 Dead world. This brings in witches and zombies into the Naruto world. Naruto and his comrades then have to use their combat skills and knowledge of their own world to combat these new threats. Along the way, they might discover that there are some similarities between the chakra system and the magic in the Left 4 Dead world that could be used to their advantage in fighting the witches and zombies.
A plotline could involve a witch from the Left 4 Dead universe being summoned to the Naruto world. This causes chaos as the characters in Naruto have no idea how to deal with this strange new entity. They have to figure out her powers and how to stop her from causing too much destruction. At the same time, some of the Naruto characters might get dragged into the Left 4 Dead world in the process of trying to stop her. There, they team up with the survivors in that world to fight against the hordes of zombies and other witches.
One possible plotline could be Naruto finding unexpected allies during his time left for dead. Maybe some characters who previously had no connection to him come to his aid out of a newfound sense of justice or a change of heart.
Another plotline might involve Naruto's inner struggle and growth. He could discover new powers or a deeper understanding of his ninja way while on the verge of death. He might have to rely solely on his wits and the training he's had in the past to survive. For example, he could use his shadow clones in more creative and strategic ways to defend himself and find a way back to his village.
One possible plotline could be that Hermione was attacked by a group of dark wizards while on a solo mission. They might have been after some knowledge she possessed. After the attack, she could be found by a mysterious figure who nurses her back to health and together they seek revenge.
One possible plotline could be Naruto's struggle with abandonment issues. Since Kushina left, Naruto might have a harder time finding his place in the village. He could become more withdrawn and have to fight even harder to prove himself. Another could be the search for Kushina. Naruto might embark on a journey to find out why she left and try to bring her back.
One idea could be a story where the Hunter and the Witch form an unlikely alliance in the post - apocalyptic world of Left 4 Dead 2. Maybe they realize that they are both being hunted by a new, more powerful enemy that has emerged. They could start to work together, using their unique abilities to survive and fight back.
One possible reason could be a misunderstanding. Maybe they were misled by false information or an enemy's trickery that made them think Naruto was a threat at that moment. Another reason might be extreme pressure or a life - or - death situation where they thought sacrificing Naruto was the only way to save the rest of the team or complete a crucial mission.
Perhaps there was some sort of dark influence or mind - control at play. An enemy might have manipulated Kakashi's mind in such a way that he believed Naruto was a threat and thus left him for dead, not realizing his true self.
Well, there could be a plotline where Naruto's ability to see the dead is initially seen as a curse. He struggles with it until he meets an old sage who tells him it's actually a great gift. Then he starts to explore the spiritual side of the ninja world more deeply. He might also use his power to help the families of the dead find closure. For instance, he could pass on messages from the dead loved ones, which would earn him the respect and love of many in the village.
One idea could be a story where the Hunter and the Witch form an unlikely alliance. Maybe they find themselves in a situation where they both need to survive against a new and more powerful enemy that has emerged in the post - apocalyptic world of Left 4 Dead. They start to understand each other's motives and abilities, and through their cooperation, they discover new ways to fight back.
I'm not sure of specific ones off the top of my head. But you can try searching on fanfiction websites like Archive of Our Own. There might be some unique crossovers there that combine the elements of Naruto, witches, and Left 4 Dead in interesting ways.