One idea could be that Naruto, with his ninja skills, somehow gets involved in the world of Spy x Family. Maybe he's sent on a mission to assist Loid in a particularly dangerous espionage task. Another could be a crossover where Anya, using her telepathic powers, discovers Naruto's big secret about being a jinchuriki.
Well, Spy x Family fanfiction can be really interesting. Some fanfictions might explore different relationships between the characters in more depth. For example, they could focus on the bond between Anya and Loid in a new situation that wasn't shown in the original manga or anime. It's also fun to see how authors play with the spy and assassin themes in unique ways.
Loid would also be an engaging character to center on. His spy skills and ability to adapt to any situation could be really cool in the Naruto world. He could use his disguise and infiltration skills to gather information about the ninja clans or even help Naruto on a mission. His calm and calculated nature would be a contrast to the more impulsive and emotional nature of some of the Naruto characters.
One great AnyaxDamian fanfiction is 'A New Bond'. It beautifully explores their relationship as they are paired for a school project. The author does an amazing job of showing Anya's innocence and Damian's pride slowly melting away as they get to know each other better. It's a heartwarming read that stays true to the characters' personalities from the Spy x Family series.
One characteristic is the focus on Anya's innocence. Most fanfictions highlight her child - like view of the world despite her secret powers. For example, in many stories, she might misunderstand a situation in a really cute way.
Spy x Family manga has wrapped up. It provided a conclusive and fulfilling storyline that wrapped up all the loose ends. Now you can binge-read the entire series without any interruptions.