Yes, there are some. You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'roxas x date a live' and you'll find various stories. Some might be more to your taste in terms of writing style, plot, or character development.
You can expect a crossover of two different fictional universes. It might blend the elements of the Kingdom Hearts world where Roxas is from and the Date A Live world. There could be new storylines involving the characters from both, and perhaps some interesting power combinations or interactions.
A great fanfic in this crossover genre is 'Date A Ninja'. In this story, the Date A Live characters are quite intrigued by Naruto's world. They learn about ninjutsu and how Naruto's world is full of hidden powers. Meanwhile, Naruto has to adapt to the rules of the Date A Live world regarding spirits. It's a story full of cultural clashes and interesting character interactions.
I've read a fanfic where the Keyblade wielders from Kingdom Hearts end up in the world of Date A Live. It's called 'Keyblades in the Spirit World'. It has some really cool fight scenes and interesting character interactions as they try to find a way back home while also dealing with the Spirits.
Another aspect that makes it appealing is the chance to see how characters from different backgrounds interact. The characters in Naruto are used to a certain type of combat and way of life. When they meet the characters from Date A Live, who have different goals and ways of dealing with threats, it can lead to some really interesting storylines. For instance, Shido from Date A Live might learn some new combat techniques from Naruto, and Naruto could learn about the emotional side of dealing with spirits from Shido. This cross - pollination of ideas and skills is really engaging for readers.
Characterization is key. The fanfic should stay true to the personalities of the characters from both series. In a good fanfic, Yozora from Kingdom Hearts would retain his cool and mysterious nature when interacting with the Date A Live girls. Also, the plot should be engaging, perhaps involving a common threat that requires the combined efforts of both sets of characters to overcome.
The theme of self - discovery is also present. Through their relationship, both Roxas and Xaldin learn more about themselves. For example, Roxas might discover a darker side of himself, and Xaldin could find a bit of softness. It's about how they change because of each other. And also, the theme of loyalty often comes up. How far are they willing to go for each other in this rather unique relationship?
One common theme is friendship. Many fanfics explore how their initial friendship develops into something deeper. For example, they might start as comrades in a difficult situation and gradually realize their feelings for each other.
I'm sorry, but I don't have specific 'roxas x xion lemon fanfic' to recommend directly. You can try searching on fanfic - specific websites like Archive of Our Own (AO3). They usually have a large collection of fan - made stories related to various characters.
A sense of belonging is another common theme. They find a sense of home and acceptance in each other. It's about two characters who are a bit lost on their own but together, they form a complete unit, and fanfics often play with this idea.