No. Fanfictions are supposed to be creative works that respect the source material and its fan base. The idea presented in this title goes against the general values associated with Pokémon. Pokémon fanfics usually center around things like Ash's journey, his battles, and his relationships with his Pokémon and friends in a positive and appropriate way.
One appropriate topic could be a crossover fanfic where Pokémon characters interact with characters from another popular franchise in a positive and family - friendly way. For example, Pokémon meeting characters from the Studio Ghibli universe. Or a fanfic that focuses on the backstories of the Gym Leaders, like how they became Gym Leaders, their training regimens, and their dreams for their respective Gyms and the Pokémon trainers who come to challenge them.
Since we have so little information from just this title, it could be a symbolic piece. The 'ash' might represent something like decay or the end of something, and the 'leaf' could be a symbol of life or nature. And the 'cums' might be an odd way of indicating that the ash is gathering or coming together inside the leaf in the context of the story.
I'm not entirely clear on the exact concept just from this title. It could be about the physical process of ash getting inside a leaf in a fictional scenario.
Perhaps Ash and Cybthia are part of a secret organization. They are assigned on a dangerous mission together. During the mission, they discover new sides of each other. Cybthia gets injured and Ash takes care of her. This closeness results in a strong emotional and physical bond, which could form the basis of the 'ash cums inside cybthia' aspect in a tasteful and consensual way within the story.
I'm not sure if there is a specific 'Cums Inside Kushina' fanfic. Fanfics cover a wide range of themes and stories, but this might be a rather inappropriate or hard - to - find one. It also depends on the specific fanfic platforms and their content policies.
I'm not aware of any such fanfic, and this kind of description involves inappropriate and vulgar content. Fanfics should generally be based on positive, creative and appropriate themes.
First, start with them having common interests or goals. For example, if they are in a competitive field, they could start as rivals and gradually respect each other's skills. Then, through shared experiences like going through a tough training session together or facing a common enemy. This would build a foundation for their relationship to grow. And when it comes to the more intimate part, it should be a natural result of the deep emotional connection they've developed.
Most platforms have strict rules against fanfics that contain pornographic or vulgar content. So it's very unlikely that you'll find a legitimate 'Naruto Cums Inside Karin' fanfic in proper fanfic communities.