The characters from Danmachi could have a range of reactions to Fate fanfiction. Some might be confused at first, especially if the fanfiction has very complex Fate lore. However, those who are more open - minded, like Bell, might be excited to explore new stories and ideas. He could see similarities in the way heroes are portrayed in both worlds and be inspired by it.
One way a Danmachi - Fate fanfiction crossover could function is through the concept of parallel universes. The two universes could be connected in some way, and certain events could cause portals to open between them. In this scenario, the adventurers from Danmachi would enter the Fate world. They would be faced with the complex politics and power struggles there. The Fate characters might view the Danmachi characters as strange new entities. There could be a lot of misunderstandings at first, but as they get to know each other, they could learn from each other's strengths. For example, the Danmachi characters could learn about the strategic use of Command Spells from the Fate characters, while the Fate characters could be impressed by the physical combat skills of the Danmachi adventurers.
One great 'Danmachi Aiz x Bell Fanfic' is 'The Encounter'. It beautifully portrays the relationship between Aiz and Bell. The story focuses on how they train together and gradually develop deeper feelings for each other. The author does a wonderful job of capturing the essence of their characters from the original series.
A frequently seen theme is the exploration of Freya's obsessive love for Bell. It shows how her feelings can be both a source of strength and a potential danger for Bell. Also, the theme of destiny plays a role. Many fanfics explore whether Bell and Freya are fated to be together or if their different statuses will keep them apart. The stories often play with the idea of how much they can defy destiny or if they are bound by it.
A really cool concept for a 'naruto x danmachi fanfiction' could be that the tailed beasts exist in the Danmachi world but are sealed away in the deepest parts of the dungeons. Naruto has to team up with Bell Cranel and other adventurers to either free or reseal them. Along the way, Naruto shows them his ninja techniques and they in turn teach him about the magic and skills specific to the Danmachi world. This would create a great dynamic between the two different universes and their respective powers.
One great 'danmachi freya x bell fanfic' is 'Freya's Obsession'. It delves into Freya's complex feelings for Bell in a very interesting way. The author does a wonderful job of portraying their interactions within the world of Danmachi.
A common theme is the growth of their relationship. It could be a slow - burn type of relationship where they gradually become closer. Another theme is adventure, as they often go on dungeon crawls together in the fanfictions.
You can start by looking on fanfiction.net. It has a large collection of 'Danmachi' fanfics, including many centered around Aiz and Bell. Just use the search bar and type in relevant keywords like 'Danmachi Aiz x Bell' and you'll get a list of available fanfics.