There's this 'Spy x Sniper TF2 Fanfic' called 'The Hidden Alliance'. It's really interesting because it reveals the hidden feelings and unspoken agreements between Spy and Sniper. A lot of these fanfics explore their personalities. For example, some fanfics might show Spy's cunning nature and Sniper's calm and collected demeanor in different ways. 'The Covert Operation' is another fanfic that plays around with their relationship in a thrilling plot.
I think 'A Tale of Two Mercenaries: Spy and Sniper' is a must - read 'Spy x Sniper TF2 Fanfic'. It begins by setting up their initial encounters and how they gradually start to trust each other more. The story is full of action - packed scenes that are typical of the TF2 universe. There are also some really well - written descriptions of their weapons and gear, which adds to the authenticity. Another fanfic, 'The Sniper's Secret Watcher', is great for those who like a bit of mystery in their fanfics. It keeps you guessing about Spy's motives regarding Sniper throughout the story.